diff --git a/.gitignore b/.gitignore
index b858aca..741f1b4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,14 +1,114 @@
-.env
-.venv
-__pycache__
-
 /build
 /dist
 /docs/_build
 /pack
+htmlcov/
+.pytest_cache/
+.vscode/
+
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
 
-*.egg-info
+# Distribution / packaging
+.Python
+develop-eggs/
+downloads/
+eggs/
+.eggs/
+sdist/
+var/
+wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+MANIFEST
 
-*.py[co]
+# PyInstaller
+#  Usually these files are written by a python script from a template
+#  before PyInstaller builds the exe, so as to inject date/other infos into it.
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.nox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+.hypothesis/
 .pytest_cache/
-.vscode/
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+local_settings.py
+db.sqlite3
+
+# Flask stuff:
+instance/
+.webassets-cache
+
+# Scrapy stuff:
+.scrapy
+
+# Sphinx documentation
+docs/_build/
+
+# PyBuilder
+target/
+
+# Jupyter Notebook
+.ipynb_checkpoints
+
+# IPython
+profile_default/
+ipython_config.py
+
+# pyenv
+.python-version
+
+# celery beat schedule file
+celerybeat-schedule
+
+# SageMath parsed files
+*.sage.py
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# Spyder project settings
+.spyderproject
+.spyproject
+
+# Rope project settings
+.ropeproject
+
+# mkdocs documentation
+/site
+
+# mypy
+.mypy_cache/
+.dmypy.json
+dmypy.json
diff --git a/.travis.yml b/.travis.yml
index 8e38f96..3acd3a4 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,8 +7,8 @@ matrix:
   fast_finish: true
 
 install:
-  - "python -m pip install --upgrade pip pytest-timeout"
-  - "python -m pip install --upgrade -e .[tests]"
+  - "python -m pip install --upgrade pip setuptools pytest-timeout"
+  - "python -m pip install --upgrade -e .[tests,virtualenv]"
 script:
   - "python -m pytest -v -n 8 tests/"
 
@@ -24,7 +24,7 @@ jobs:
     - stage: packaging
       python: "3.6"
       install:
-        - "python -m pip install --upgrade pip"
+        - "python -m pip install --upgrade pip setuptools"
         - "python -m pip install --upgrade check-manifest readme-renderer"
       script:
         - "python setup.py check -m -r -s"
@@ -38,8 +38,7 @@ jobs:
     - stage: coverage
       python: "3.6"
       install:
-        - "python -m pip install --upgrade pip"
-        - "python -m pip install --upgrade -e .[tests]"
-        - "python -m pip install --upgrade pytest-timeout pytest-xdist pytest-cov"
+        - "python -m pip install --upgrade pip setuptools pytest-timeout pytest-cov pytest-xdist"
+        - "python -m pip install --upgrade -e .[tests,virtualenv]"
       script:
         - "pytest -n auto --timeout 300 --cov=passa --cov-report=term-missing --cov-report=xml --cov-report=html tests"
diff --git a/Pipfile b/Pipfile
index d81fba9..6356718 100644
--- a/Pipfile
+++ b/Pipfile
@@ -1,5 +1,5 @@
 [packages]
-passa = { editable = true, path = '.' }
+passa = {editable = true,path = '.',extras = ['virtualenv']}
 
 # Override sdist-only dependency via TOMLkit to fix build. (sarugaku/passa#61)
 [packages.functools32]
@@ -12,12 +12,13 @@ markers = "python_version < '3.0'"
 black = '*'
 invoke = '*'
 parver = '*'
-passa = { editable = true, path = '.', extras = ['tests'] }
+passa = {editable = true,path = '.',extras = ['tests']}
 sphinx = '*'
 sphinx-rtd-theme = '*'
 towncrier = '*'
 twine = '*'
 wheel = '*'
+coverage = "<5.0"
 
 [scripts]
 passa-add = 'python -m passa.cli.add'
@@ -25,7 +26,6 @@ passa-remove = 'python -m passa.cli.remove'
 passa-upgrade = 'python -m passa.cli.upgrade'
 passa-lock = 'python -m passa.cli.lock'
 passa-freeze = 'python -m passa.cli.freeze'
-
 black = 'black src/passa/ --exclude "/(\.git|\.hg|\.mypy_cache|\.tox|\.venv|_build|buck-out|build|dist)/"'
 build = 'inv build'
 changelog = 'towncrier'
@@ -34,3 +34,6 @@ draft = 'towncrier --draft'
 release = 'inv release'
 tests = "pytest -v tests"
 upload = 'inv upload'
+
+[pipenv]
+allow_prereleases = true
diff --git a/Pipfile.lock b/Pipfile.lock
index 624bd15..6dca024 100644
--- a/Pipfile.lock
+++ b/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "98ad4ec51e7ea8861ce2e31ac6d39a134251d84a2a7b47f2053e905900312639"
+            "sha256": "2c60c86f5fbcfab3b4b94e06a793479341cd462c3868f40ca1efffd795ad9a20"
         },
         "pipfile-spec": 6,
         "requires": {},
@@ -19,7 +19,6 @@
                 "sha256:9e5896d1372858f8dd3344faf4e5014d21849c756c8d5701f78f8a103b372d92",
                 "sha256:d8b24664561d0d34ddfaec54636d502d7cea6e29c3eaf68f3df6180863e2166e"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version >= '3.6'",
             "version": "==1.4.3"
         },
         "attrs": {
@@ -27,7 +26,6 @@
                 "sha256:10cbf6e27dbce8c30807caf056c8eb50917e0eaafe86347671b57254006c3e69",
                 "sha256:ca4be454458f9dec299268d472aaa5a11f67a4ff70093396e1ceae9c76cf4bbb"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version >= '3.6'",
             "version": "==18.2.0"
         },
         "backports-functools-lru-cache": {
@@ -51,11 +49,17 @@
             "markers": "python_version < '3.3' and python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.0.post1"
         },
+        "cached-property": {
+            "hashes": [
+                "sha256:3a026f1a54135677e7da5ce819b0c690f156f37976f3e30c5430740725203d7f",
+                "sha256:9217a59f14a5682da7c4b8829deadbfc194ac22e9908ccf7c8820234e80a1504"
+            ],
+            "version": "==1.5.1"
+        },
         "cerberus": {
             "hashes": [
                 "sha256:f5c2e048fb15ecb3c088d192164316093fcfa602a74b3386eefb2983aa7e800a"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.2"
         },
         "certifi": {
@@ -63,7 +67,6 @@
                 "sha256:47f9c83ef4c0c621eaef743f133f09fa8a74a9b75f037e8624f83bd1b6626cb7",
                 "sha256:993f830721089fef441cdfeb4b2c8c9df86f0c63239f06bd025a76a7daddb033"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==2018.11.29"
         },
         "chardet": {
@@ -71,7 +74,6 @@
                 "sha256:84ab92ed1c4d4f16916e05906b6b75a6c0fb5db821cc65e70cbd64a3e2a5eaae",
                 "sha256:fc323ffcaeaed0e0a02bf4d117757b98aed530d9ed4531e3e15460124c106691"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==3.0.4"
         },
         "colorama": {
@@ -79,21 +81,18 @@
                 "sha256:05eed71e2e327246ad6b38c540c4a3117230b19679b875190486ddd2d721422d",
                 "sha256:f8ac84de7840f5b9c4e3347b3c1eaa50f7e49c2b07596221daec5edaabbd7c48"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' and sys_platform == 'win32' or python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3' and sys_platform == 'win32'",
             "version": "==0.4.1"
         },
         "cursor": {
             "hashes": [
                 "sha256:8ee9fe5b925e1001f6ae6c017e93682583d2b4d1ef7130a26cfcdf1651c0032c"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.2.0"
         },
         "distlib": {
             "hashes": [
                 "sha256:57977cd7d9ea27986ec62f425630e4ddb42efe651ff80bc58ed8dbc3c7c21f19"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.2.8"
         },
         "enum34": {
@@ -111,39 +110,57 @@
                 "sha256:3bb3de3582cb27071cfb514f00ed784dc444b7f96dc21e140de65fe00585c95e",
                 "sha256:41d5b64e70507d0c3ca742d68010a76060eea8a3d863e9b5130ab11a4a91aa0e"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==2.0.1"
         },
         "functools32": {
             "file": "https://github.com/sarugaku/functools32/releases/download/3.2.3-2/functools32-3.2.3.post2-py2.py3-none-any.whl",
-            "markers": "python_version < '3.0' or python_version < '3.0' and python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version < '3.0' and python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'"
+            "hashes": [
+                "sha256:89d824aa6c358c421a234d7f9ee0bd75933a67c29588ce50aaa3acdf4d403fa0",
+                "sha256:f6253dfbe0538ad2e387bd8fdfd9293c925d63553f5813c4e587745416501e6d"
+            ],
+            "markers": "python_version < '3.0'",
+            "version": "==3.2.3.post2"
         },
         "idna": {
             "hashes": [
-                "sha256:156a6814fb5ac1fc6850fb002e0852d56c0c8d2531923a51032d1b70760e186e",
-                "sha256:684a38a6f903c1d71d6d5fac066b58d7768af4de2b832e426ec79c30daa94a16"
+                "sha256:c357b3f628cf53ae2c4c05627ecc484553142ca23264e593d327bcde5e9c3407",
+                "sha256:ea8b7f6188e6fa117537c3df7da9fc686d485087abf6ac197f9c46432f7e4a3c"
+            ],
+            "version": "==2.8"
+        },
+        "installer": {
+            "hashes": [
+                "sha256:1ba23de573e9b95a8dcbd04fd026c40a64b77db0aadc48f28a844b4cb87479fe",
+                "sha256:f4f195c9b17ea7d2b631a758451485c6b080975349b4adebe45ef4bb022db069"
+            ],
+            "version": "==0.1.1"
+        },
+        "mork": {
+            "hashes": [
+                "sha256:13772edb4724915cf0cfa30d31426e0565487a3b2d7883b8468718eaed8ecfc2",
+                "sha256:b1b41bc31603eef1b50e42e75ae2d74d7a0d9ab46ea4d0dd1ba387a451870873"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
-            "version": "==2.7"
+            "version": "==0.1.4"
         },
-        "importlib": {
+        "packagebuilder": {
             "hashes": [
-                "sha256:b6ee7066fea66e35f8d0acee24d98006de1a0a8a94a8ce6efe73a9a23c8d9826"
+                "sha256:1e85c4e0e994322996b93cd6685c12834d30f3558889154f8e3de8fb1f3fd1e7",
+                "sha256:dc525d06ecd102db23ab421b879d7d27021d784ff933e33e8c411a53af5c9dbe"
             ],
-            "markers": "python_version < '2.7' and python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
-            "version": "==1.0.4"
+            "version": "==0.1.0"
         },
         "packaging": {
             "hashes": [
                 "sha256:0886227f54515e592aaa2e5a553332c73962917f2831f1b0f9b9f4380a4b9807",
                 "sha256:f95a1e147590f204328170981833854229bb2912ac3d5f89e2a8ccd2834800c9"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==18.0"
         },
         "passa": {
             "editable": true,
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
+            "extras": [
+                "virtualenv"
+            ],
             "path": "."
         },
         "pathlib2": {
@@ -159,7 +176,6 @@
                 "sha256:cc663a438fdfe2e88d8d3c5ef2203ac858de34e31b6609b1fc505d611490a926",
                 "sha256:f79bb08fb064dfc5b141204bfeb56a4141a6d504677fab4723036a464fc25cc1"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.3"
         },
         "pip-shims": {
@@ -167,7 +183,6 @@
                 "sha256:3bc24ec050a6b9eea35419467237e4f47eaf806dadc9999bf887355c377edea7",
                 "sha256:edb4cf3c509eab2f36b55c1ac1a59a4c485ccd537cc87934d74950880f641256"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.3.2"
         },
         "plette": {
@@ -178,7 +193,6 @@
                 "sha256:c0e3553c1e581d8423daccbd825789c6e7f29b7d9e00e5331b12e1642a1a26d3",
                 "sha256:dde5d525cf5f0cbad4d938c83b93db17887918daf63c13eafed257c4f61b07b4"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.2.2"
         },
         "pyparsing": {
@@ -186,30 +200,33 @@
                 "sha256:40856e74d4987de5d01761a22d1621ae1c7f8774585acae358aa5c5936c6c90b",
                 "sha256:f353aab21fd474459d97b709e527b5571314ee5f067441dc9f88e33eecd96592"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==2.3.0"
         },
         "pytoml": {
             "hashes": [
                 "sha256:ca2d0cb127c938b8b76a9a0d0f855cf930c1d50cc3a0af6d3595b566519a1013"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.1.20"
         },
+        "recursive-monkey-patch": {
+            "hashes": [
+                "sha256:546739fea5be2ea9f98b5ec44fafeb697b5cf9fdcda64a03422582ab03ee24c4",
+                "sha256:98922554e77f2e2c85a4f5d873a0f52efdc1b553f32444bd6c788b2ff583bf3e"
+            ],
+            "version": "==0.4.0"
+        },
         "requests": {
             "hashes": [
-                "sha256:65b3a120e4329e33c9889db89c80976c5272f56ea92d3e74da8a463992e3ff54",
-                "sha256:ea881206e59f41dbd0bd445437d792e43906703fff75ca8ff43ccdb11f33f263"
+                "sha256:502a824f31acdacb3a35b6690b5fbf0bc41d63a24a45c4004352b0242707598e",
+                "sha256:7bf2a778576d825600030a110f3c0e3e8edc51dfaafe1c146e39a2027784957b"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
-            "version": "==2.20.1"
+            "version": "==2.21.0"
         },
         "requirementslib": {
             "hashes": [
                 "sha256:c2c00c7bd3bd4984c97d10cd4d143efbe33b5ed9e55961bea30ca7a9a4927289",
                 "sha256:dc6b692e8dee03d6e90c29db1e337b0bf8152cce84a57f0fb4765e596afde4e0"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.3.3"
         },
         "resolvelib": {
@@ -217,7 +234,6 @@
                 "sha256:6c4c6690b0bdd78bcc002e1a5d1b6abbde58c694a6ea1838f165b20d2c943db7",
                 "sha256:8734e53271ef98f38a2c99324d5e7905bc00c97dc3fc5bb7d83c82a979e71c04"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.2.2"
         },
         "scandir": {
@@ -239,17 +255,16 @@
         },
         "six": {
             "hashes": [
-                "sha256:70e8a77beed4562e7f14fe23a786b54f6296e34344c23bc42f07b15018ff98e9",
-                "sha256:832dc0e10feb1aa2c68dcc57dbb658f1c7e65b9b61af69048abc87a2db00a0eb"
+                "sha256:3350809f0555b11f552448330d0b52d5f24c91a322ea4a15ef22629740f3761c",
+                "sha256:d16a0141ec1a18405cd4ce8b4613101da75da0e9a7aec5bdd4fa804d0e0eba73"
             ],
-            "version": "==1.11.0"
+            "version": "==1.12.0"
         },
         "tomlkit": {
             "hashes": [
                 "sha256:d6506342615d051bc961f70bfcfa3d29b6616cc08a3ddfd4bc24196f16fd4ec2",
                 "sha256:f077456d35303e7908cc233b340f71e0bec96f63429997f38ca9272b7d64029e"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.5.3"
         },
         "typing": {
@@ -258,7 +273,7 @@
                 "sha256:57dcf675a99b74d64dacf6fba08fb17cf7e3d5fdff53d4a30ea2a5e7e52543d4",
                 "sha256:a4c8473ce11a65999c8f59cb093e70686b6c84c98df58c1dae9b3b196089858a"
             ],
-            "markers": "python_version < '3.5' and python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version < '3.5' and python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
+            "markers": "(python_version >= '2.7' and python_version < '2.8') or (python_version >= '3.4' and python_version < '3.5') and python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or (python_version >= '2.7' and python_version < '2.8') or (python_version >= '3.4' and python_version < '3.5') and python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==3.6.6"
         },
         "urllib3": {
@@ -266,9 +281,15 @@
                 "sha256:61bf29cada3fc2fbefad4fdf059ea4bd1b4a86d2b6d15e1c7c0b582b9752fe39",
                 "sha256:de9529817c93f27c8ccbfead6985011db27bd0ddfcdb2d86f3f663385c6a9c22"
             ],
-            "markers": "python_version < '4' and python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version < '4' and python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.24.1"
         },
+        "virtualenv": {
+            "hashes": [
+                "sha256:686176c23a538ecc56d27ed9d5217abd34644823d6391cbeb232f42bf722baad",
+                "sha256:f899fafcd92e1150f40c8215328be38ff24b519cd95357fa6e78e006c7638208"
+            ],
+            "version": "==16.1.0"
+        },
         "vistir": {
             "extras": [
                 "spinner"
@@ -277,7 +298,6 @@
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@@ -285,7 +305,6 @@
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@@ -293,7 +312,6 @@
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@@ -311,7 +328,6 @@
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@@ -319,7 +335,6 @@
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@@ -327,7 +342,6 @@
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@@ -403,7 +419,6 @@
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@@ -411,7 +426,6 @@
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@@ -464,21 +509,18 @@
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@@ -504,7 +546,6 @@
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@@ -512,7 +553,6 @@
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@@ -523,33 +563,38 @@
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@@ -557,6 +602,13 @@
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@@ -603,7 +655,6 @@
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@@ -612,15 +663,20 @@
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@@ -628,15 +684,13 @@
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@@ -652,7 +706,6 @@
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@@ -660,7 +713,6 @@
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@@ -678,7 +730,6 @@
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             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.2.2"
         },
         "pluggy": {
@@ -686,7 +737,6 @@
                 "sha256:447ba94990e8014ee25ec853339faf7b0fc8050cdc3289d4d71f7f410fb90095",
                 "sha256:bde19360a8ec4dfd8a20dcb811780a30998101f078fc7ded6162f0076f50508f"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.8.0"
         },
         "py": {
@@ -694,9 +744,15 @@
                 "sha256:bf92637198836372b520efcba9e020c330123be8ce527e535d185ed4b6f45694",
                 "sha256:e76826342cefe3c3d5f7e8ee4316b80d1dd8a300781612ddbc765c17ba25a6c6"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.7.0"
         },
+        "pycparser": {
+            "hashes": [
+                "sha256:a988718abfad80b6b157acce7bf130a30876d27603738ac39f140993246b25b3"
+            ],
+            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
+            "version": "==2.19"
+        },
         "pygments": {
             "hashes": [
                 "sha256:6301ecb0997a52d2d31385e62d0a4a4cf18d2f2da7054a5ddad5c366cd39cee7",
@@ -709,7 +765,6 @@
                 "sha256:40856e74d4987de5d01761a22d1621ae1c7f8774585acae358aa5c5936c6c90b",
                 "sha256:f353aab21fd474459d97b709e527b5571314ee5f067441dc9f88e33eecd96592"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==2.3.0"
         },
         "pytest": {
@@ -717,7 +772,6 @@
                 "sha256:1d131cc532be0023ef8ae265e2a779938d0619bb6c2510f52987ffcba7fa1ee4",
                 "sha256:ca4761407f1acc85ffd1609f464ca20bb71a767803505bd4127d0e45c5a50e23"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==4.0.1"
         },
         "pytest-cov": {
@@ -725,7 +779,6 @@
                 "sha256:513c425e931a0344944f84ea47f3956be0e416d95acbd897a44970c8d926d5d7",
                 "sha256:e360f048b7dae3f2f2a9a4d067b2dd6b6a015d384d1577c994a43f3f7cbad762"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==2.6.0"
         },
         "pytest-forked": {
@@ -733,7 +786,6 @@
                 "sha256:e4500cd0509ec4a26535f7d4112a8cc0f17d3a41c29ffd4eab479d2a55b30805",
                 "sha256:f275cb48a73fc61a6710726348e1da6d68a978f0ec0c54ece5a5fae5977e5a08"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.2"
         },
         "pytest-timeout": {
@@ -741,7 +793,6 @@
                 "sha256:4a30ba76837a32c7b7cd5c84ee9933fde4b9022b0cd20ea7d4a577c2a1649fb1",
                 "sha256:d49f618c6448c14168773b6cdda022764c63ea80d42274e3156787e8088d04c6"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.3.3"
         },
         "pytest-xdist": {
@@ -749,14 +800,12 @@
                 "sha256:5e8b68466c057f0f37e36909612f8838e518ce703c8da31f85e47c7dea8acc93",
                 "sha256:909bb938bdb21e68a28a8d58c16a112b30da088407b678633efb01067e3923de"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.24.1"
         },
         "pytoml": {
             "hashes": [
                 "sha256:ca2d0cb127c938b8b76a9a0d0f855cf930c1d50cc3a0af6d3595b566519a1013"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.1.20"
         },
         "pytz": {
@@ -764,7 +813,6 @@
                 "sha256:31cb35c89bd7d333cd32c5f278fca91b523b0834369e757f4c5641ea252236ca",
                 "sha256:8e0f8568c118d3077b46be7d654cc8167fa916092e28320cde048e54bfc9f1e6"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==2018.7"
         },
         "readme-renderer": {
@@ -774,13 +822,19 @@
             ],
             "version": "==24.0"
         },
+        "recursive-monkey-patch": {
+            "hashes": [
+                "sha256:546739fea5be2ea9f98b5ec44fafeb697b5cf9fdcda64a03422582ab03ee24c4",
+                "sha256:98922554e77f2e2c85a4f5d873a0f52efdc1b553f32444bd6c788b2ff583bf3e"
+            ],
+            "version": "==0.4.0"
+        },
         "requests": {
             "hashes": [
-                "sha256:65b3a120e4329e33c9889db89c80976c5272f56ea92d3e74da8a463992e3ff54",
-                "sha256:ea881206e59f41dbd0bd445437d792e43906703fff75ca8ff43ccdb11f33f263"
+                "sha256:502a824f31acdacb3a35b6690b5fbf0bc41d63a24a45c4004352b0242707598e",
+                "sha256:7bf2a778576d825600030a110f3c0e3e8edc51dfaafe1c146e39a2027784957b"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
-            "version": "==2.20.1"
+            "version": "==2.21.0"
         },
         "requests-toolbelt": {
             "hashes": [
@@ -794,7 +848,6 @@
                 "sha256:c2c00c7bd3bd4984c97d10cd4d143efbe33b5ed9e55961bea30ca7a9a4927289",
                 "sha256:dc6b692e8dee03d6e90c29db1e337b0bf8152cce84a57f0fb4765e596afde4e0"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.3.3"
         },
         "resolvelib": {
@@ -802,39 +855,20 @@
                 "sha256:6c4c6690b0bdd78bcc002e1a5d1b6abbde58c694a6ea1838f165b20d2c943db7",
                 "sha256:8734e53271ef98f38a2c99324d5e7905bc00c97dc3fc5bb7d83c82a979e71c04"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.2.2"
         },
-        "scandir": {
-            "hashes": [
-                "sha256:04b8adb105f2ed313a7c2ef0f1cf7aff4871aa7a1883fa4d8c44b5551ab052d6",
-                "sha256:1444134990356c81d12f30e4b311379acfbbcd03e0bab591de2696a3b126d58e",
-                "sha256:1b5c314e39f596875e5a95dd81af03730b338c277c54a454226978d5ba95dbb6",
-                "sha256:346619f72eb0ddc4cf355ceffd225fa52506c92a2ff05318cfabd02a144e7c4e",
-                "sha256:44975e209c4827fc18a3486f257154d34ec6eaec0f90fef0cca1caa482db7064",
-                "sha256:61859fd7e40b8c71e609c202db5b0c1dbec0d5c7f1449dec2245575bdc866792",
-                "sha256:a5e232a0bf188362fa00123cc0bb842d363a292de7126126df5527b6a369586a",
-                "sha256:c14701409f311e7a9b7ec8e337f0815baf7ac95776cc78b419a1e6d49889a383",
-                "sha256:c7708f29d843fc2764310732e41f0ce27feadde453261859ec0fca7865dfc41b",
-                "sha256:c9009c527929f6e25604aec39b0a43c3f831d2947d89d6caaab22f057b7055c8",
-                "sha256:f5c71e29b4e2af7ccdc03a020c626ede51da471173b4a6ad1e904f2b2e04b4bd"
-            ],
-            "markers": "python_version < '3.5' and python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version < '3.5' and python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
-            "version": "==1.9.0"
-        },
         "six": {
             "hashes": [
-                "sha256:70e8a77beed4562e7f14fe23a786b54f6296e34344c23bc42f07b15018ff98e9",
-                "sha256:832dc0e10feb1aa2c68dcc57dbb658f1c7e65b9b61af69048abc87a2db00a0eb"
+                "sha256:3350809f0555b11f552448330d0b52d5f24c91a322ea4a15ef22629740f3761c",
+                "sha256:d16a0141ec1a18405cd4ce8b4613101da75da0e9a7aec5bdd4fa804d0e0eba73"
             ],
-            "version": "==1.11.0"
+            "version": "==1.12.0"
         },
         "snowballstemmer": {
             "hashes": [
                 "sha256:919f26a68b2c17a7634da993d91339e288964f93c274f1343e3bbbe2096e1128",
                 "sha256:9f3bcd3c401c3e862ec0ebe6d2c069ebc012ce142cce209c098ccb5b09136e89"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.2.1"
         },
         "sphinx": {
@@ -842,7 +876,6 @@
                 "sha256:120732cbddb1b2364471c3d9f8bfd4b0c5b550862f99a65736c77f970b142aea",
                 "sha256:b348790776490894e0424101af9c8413f2a86831524bd55c5f379d3e3e12ca64"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.8.2"
         },
         "sphinx-rtd-theme": {
@@ -857,7 +890,6 @@
                 "sha256:68ca7ff70785cbe1e7bccc71a48b5b6d965d79ca50629606c7861a21b206d9dd",
                 "sha256:9de47f375baf1ea07cdb3436ff39d7a9c76042c10a769c52353ec46e4e8fc3b9"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.1.0"
         },
         "toml": {
@@ -872,7 +904,6 @@
                 "sha256:d6506342615d051bc961f70bfcfa3d29b6616cc08a3ddfd4bc24196f16fd4ec2",
                 "sha256:f077456d35303e7908cc233b340f71e0bec96f63429997f38ca9272b7d64029e"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.5.3"
         },
         "towncrier": {
@@ -887,7 +918,6 @@
                 "sha256:3c4d4a5a41ef162dd61f1edb86b0e1c7859054ab656b2e7c7b77e7fbf6d9f392",
                 "sha256:5b4d5549984503050883bc126280b386f5f4ca87e6c023c5d015655ad75bdebb"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1'",
             "version": "==4.28.1"
         },
         "twine": {
@@ -903,7 +933,7 @@
                 "sha256:57dcf675a99b74d64dacf6fba08fb17cf7e3d5fdff53d4a30ea2a5e7e52543d4",
                 "sha256:a4c8473ce11a65999c8f59cb093e70686b6c84c98df58c1dae9b3b196089858a"
             ],
-            "markers": "python_version < '3.5' and python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version < '3.5' and python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
+            "markers": "(python_version >= '2.7' and python_version < '2.8') or (python_version >= '3.4' and python_version < '3.5') and python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or (python_version >= '2.7' and python_version < '2.8') or (python_version >= '3.4' and python_version < '3.5') and python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==3.6.6"
         },
         "urllib3": {
@@ -911,7 +941,6 @@
                 "sha256:61bf29cada3fc2fbefad4fdf059ea4bd1b4a86d2b6d15e1c7c0b582b9752fe39",
                 "sha256:de9529817c93f27c8ccbfead6985011db27bd0ddfcdb2d86f3f663385c6a9c22"
             ],
-            "markers": "python_version < '4' and python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version < '4' and python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==1.24.1"
         },
         "vistir": {
@@ -922,7 +951,6 @@
                 "sha256:3a1020fb7be000b268af96641ced9ead844b1f75840c41e20e473647688fc630",
                 "sha256:6d2005ad670f77bd9c9b5415c4e2a4a20dce5b0cf0e0d11598eb463b2e0ebe44"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.2.5"
         },
         "webencodings": {
@@ -930,7 +958,6 @@
                 "sha256:a0af1213f3c2226497a97e2b3aa01a7e4bee4f403f95be16fc9acd2947514a78",
                 "sha256:b36a1c245f2d304965eb4e0a82848379241dc04b865afcc4aab16748587e1923"
             ],
-            "markers": "python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.5.1"
         },
         "wheel": {
@@ -938,7 +965,6 @@
                 "sha256:029703bf514e16c8271c3821806a1c171220cc5bdd325cbf4e7da1e056a01db6",
                 "sha256:1e53cdb3f808d5ccd0df57f964263752aa74ea7359526d3da6c02114ec1e1d44"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3' or python_version >= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.32.3"
         },
         "yaspin": {
@@ -946,7 +972,6 @@
                 "sha256:36fdccc5e0637b5baa8892fe2c3d927782df7d504e9020f40eb2c1502518aa5a",
                 "sha256:8e52bf8079a48e2a53f3dfeec9e04addb900c101d1591c85df69cf677d3237e7"
             ],
-            "markers": "python_version >= '2.6' and python_version not in '3.0, 3.1, 3.2, 3.3'",
             "version": "==0.14.0"
         }
     }
diff --git a/appveyor.yml b/appveyor.yml
index 3216d26..a9ecca6 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -5,8 +5,8 @@ branches:
 install:
   - "SET PATH=C:\\Python36-x64;%PATH%"
   - "python --version"
-  - "python -m pip install --upgrade pip"
-  - "python -m pip install --upgrade -e .[pack,tests]"
+  - "python -m pip install --upgrade pip setuptools pytest-timeout pytest-xdist"
+  - "python -m pip install --upgrade -e .[pack,tests,virtualenv]"
 
 build_script:
   - "python -m invoke pack"
diff --git a/docs/requirements.txt b/docs/requirements.txt
new file mode 100644
index 0000000..8213302
--- /dev/null
+++ b/docs/requirements.txt
@@ -0,0 +1,2 @@
+sphinx
+sphinx_rtd_theme
diff --git a/setup.cfg b/setup.cfg
index 98ea198..fbd97bb 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -37,13 +37,17 @@ python_requires = >=2.7,!=3.0,!=3.1,!=3.2,!=3.3
 setup_requires = setuptools>=36.2.2
 install_requires =
     appdirs
-    distlib
+    cached-property
+    distlib>=0.2.8
+    installer
+    packagebuilder
     packaging
-    pip-shims>=0.1.2
+    pip-shims>=0.3.1
     plette[validation]>=0.2.2
+    recursive-monkey-patch
     requests
+    requirementslib>=1.1.7
     resolvelib>=0.2.1,!=1.0.0.dev0
-    requirementslib>=1.1.1
     six
     vistir[spinner]>=0.1.4
 
@@ -51,6 +55,8 @@ install_requires =
 pack =
     invoke
     parver
+virtualenv =
+    mork
 tests =
     pytest-xdist
     pytest-timeout
@@ -89,13 +95,21 @@ ignore =
     # E231: missing whitespace after ','
     # E402: module level import not at top of file
     # E501: line too long
-    E127,E128,E129,E222,E231,E402,E501
+    E231,E402,E501
 
 [tool:pytest]
 strict = true
 addopts = -ra
 testpaths = tests/
 norecursedirs = .* build dist news tasks docs
+filterwarnings =
+    ignore::DeprecationWarning
+    ignore::PendingDeprecationWarning
 
 [build-system]
 requires = ["setuptools", "wheel"]
+
+[mypy]
+ignore_missing_imports=true
+follow_imports=skip
+python_version=2.7
diff --git a/src/passa/actions/add.py b/src/passa/actions/add.py
index 6338466..19471de 100644
--- a/src/passa/actions/add.py
+++ b/src/passa/actions/add.py
@@ -47,8 +47,7 @@ def add_packages(packages=[], editables=[], project=None, dev=False, sync=False,
     develop = any(lockfile_diff.develop)
 
     syncer = Synchronizer(
-        project, default=default, develop=develop,
-        clean_unneeded=clean,
+        project, default=default, develop=develop, clean_unneeded=clean
     )
     success = sync(syncer)
     if not success:
diff --git a/src/passa/actions/clean.py b/src/passa/actions/clean.py
index 3570e4d..9006f22 100644
--- a/src/passa/actions/clean.py
+++ b/src/passa/actions/clean.py
@@ -3,14 +3,15 @@
 from __future__ import absolute_import, print_function, unicode_literals
 
 
-def clean(project, dev=False):
+def clean(project, default=True, dev=False, sync=True):
     from passa.models.synchronizers import Cleaner
     from passa.operations.sync import clean
 
-    cleaner = Cleaner(project, default=True, develop=dev)
+    cleaner = Cleaner(project, default=default, develop=dev, sync=sync)
 
     success = clean(cleaner)
     if not success:
         return 1
 
-    print("Cleaned project at", project.root)
+    if sync:
+        print("Cleaned project at", project.root)
diff --git a/src/passa/actions/init.py b/src/passa/actions/init.py
index 1d9f592..bbab009 100644
--- a/src/passa/actions/init.py
+++ b/src/passa/actions/init.py
@@ -42,7 +42,7 @@ def init_project(root=None, python_version=None):
     index_urls = [parsed.index_url] + parsed.extra_index_urls
     sources = get_sources(index_urls, parsed.trusted_hosts)
     data = {
-        "sources": sources,
+        "source": sources,
         "packages": {},
         "dev-packages": {},
     }
diff --git a/src/passa/actions/install.py b/src/passa/actions/install.py
index 1728dae..9872584 100644
--- a/src/passa/actions/install.py
+++ b/src/passa/actions/install.py
@@ -30,3 +30,4 @@ def install(project=None, check=True, dev=False, clean=True):
         return 1
 
     print("Synchronized project at", project.root)
+    return 0
diff --git a/src/passa/actions/lock.py b/src/passa/actions/lock.py
index 7c09469..f661c82 100644
--- a/src/passa/actions/lock.py
+++ b/src/passa/actions/lock.py
@@ -11,7 +11,8 @@ def lock(project=None):
     locker = BasicLocker(project)
     success = lock(locker)
     if not success:
-        return
+        return 1
 
     project._l.write()
     print("Written to project at", project.root)
+    return 0
diff --git a/src/passa/actions/remove.py b/src/passa/actions/remove.py
index 158f5e6..92f6168 100644
--- a/src/passa/actions/remove.py
+++ b/src/passa/actions/remove.py
@@ -3,7 +3,7 @@
 from __future__ import absolute_import, print_function, unicode_literals
 
 
-def remove(project=None, only="default", packages=[], clean=True):
+def remove(project=None, only="default", packages=[], clean=True, sync=False):
     from passa.models.lockers import PinReuseLocker
     from passa.operations.lock import lock
 
@@ -36,3 +36,4 @@ def remove(project=None, only="default", packages=[], clean=True):
         return 1
 
     print("Cleaned project at", project.root)
+    return 0
diff --git a/src/passa/cli/add.py b/src/passa/cli/add.py
index d5596cd..2635b98 100644
--- a/src/passa/cli/add.py
+++ b/src/passa/cli/add.py
@@ -4,14 +4,14 @@
 
 from ..actions.add import add_packages
 from ._base import BaseCommand
-from .options import package_group
+from .options import package_group, clean_group
 
 
 class Command(BaseCommand):
 
     name = "add"
     description = "Add packages to project."
-    arguments = [package_group]
+    arguments = [package_group, clean_group]
 
     def run(self, options):
         if not options.editables and not options.packages:
@@ -20,7 +20,8 @@ def run(self, options):
             packages=options.packages,
             editables=options.editables,
             project=options.project,
-            dev=options.dev
+            dev=options.dev,
+            clean=options.clean
         )
 
 
diff --git a/src/passa/cli/clean.py b/src/passa/cli/clean.py
index e23d5ee..a74d814 100644
--- a/src/passa/cli/clean.py
+++ b/src/passa/cli/clean.py
@@ -4,17 +4,20 @@
 
 from ..actions.clean import clean
 from ._base import BaseCommand
-from .options import dev, no_default
+from .options import dev, no_default, sync_group
 
 
 class Command(BaseCommand):
 
     name = "clean"
     description = "Uninstall unlisted packages from the environment."
-    arguments = [dev, no_default]
+    arguments = [dev, no_default, sync_group]
 
     def run(self, options):
-        return clean(project=options.project, default=options.default, dev=options.dev)
+        return clean(
+            project=options.project, default=options.default, dev=options.dev,
+            sync=options.sync
+        )
 
 
 if __name__ == "__main__":
diff --git a/src/passa/cli/options.py b/src/passa/cli/options.py
index f20b612..bc75db6 100644
--- a/src/passa/cli/options.py
+++ b/src/passa/cli/options.py
@@ -2,14 +2,18 @@
 from __future__ import absolute_import
 
 import argparse
+import inspect
 import os
 import sys
 
+import six
 import tomlkit.exceptions
 
 import passa.models.projects
 import vistir
 
+from ..models.environments import Environment
+
 
 PYTHON_VERSION = ".".join(str(v) for v in sys.version_info[:2])
 
@@ -18,25 +22,69 @@ class Project(passa.models.projects.Project):
     def __init__(self, root, *args, **kwargs):
         root = vistir.compat.Path(root).absolute()
         pipfile = root.joinpath("Pipfile")
+        environment = kwargs.pop("environment", self.get_env())
         if not pipfile.is_file():
             raise argparse.ArgumentError(
                 "project", "{0!r} is not a Pipfile project".format(root),
             )
         try:
-            super(Project, self).__init__(root.as_posix(), *args, **kwargs)
+            super(Project, self).__init__(root.as_posix(), environment=environment,
+                                            *args, **kwargs)
         except tomlkit.exceptions.ParseError as e:
             raise argparse.ArgumentError(
                 "project", "failed to parse Pipfile: {0!r}".format(str(e)),
             )
 
+    def get_env(self):
+        if 'VIRTUAL_ENV' in os.environ:
+            return Environment(prefix=os.environ['VIRTUAL_ENV'], is_venv=True)
+        return Environment()
+
     def __name__(self):
         return "Project Root"
 
 
+class OptionMeta(type):
+
+    @property
+    def action_map(self):
+        action_map = getattr(self, '_action_map', None)
+        if not action_map:
+            self.action_map = {
+                name.strip("_").replace("Action", ""): obj
+                for name, obj in inspect.getmembers(argparse)
+                if name.startswith('_') and name.endswith('Action')
+            }
+        return self._action_map
+
+    @action_map.setter
+    def action_map(self, action_map):
+        self._action_map = action_map
+
+
+@six.add_metaclass(OptionMeta)
 class Option(object):
     def __init__(self, *args, **kwargs):
-        self.args = args
-        self.kwargs = kwargs
+        self.args = list(args)
+        self.kwargs = kwargs.copy()
+        if "dest" not in kwargs and not args[0].startswith("-"):
+            dest = list(args).pop(0)
+        else:
+            dest = kwargs.pop("dest", args[0].lstrip("-").replace("-", "_"))
+        action = kwargs.pop("action", None)
+        if not action:
+            if 'const' in kwargs:
+                action = 'store_const'
+            else:
+                action = 'store'
+        self.action = self.get_option(action, args, dest, **kwargs)
+
+    @classmethod
+    def get_option(cls, action, option_strings, dest, *args, **kwargs):
+        if action:
+            action = action.title().replace("_", "")
+            return cls.action_map[action](list(option_strings), dest, *args, **kwargs)
+        return
 
     def add_to_parser(self, parser):
         parser.add_argument(*self.args, **self.kwargs)
@@ -68,6 +116,9 @@ def add_to_parser(self, parser):
         self.argument_group = group
         self.parser = parser
 
+    def add_to_group(self, group):
+        self.add_to_parser(group)
+
 
 project = Option(
     "--project", metavar="project", default=os.getcwd(), type=Project,
@@ -80,7 +131,7 @@ def add_to_parser(self, parser):
 )
 
 python_version = Option(
-    "--py-version", "--python-version", "--requires-python", metavar="python-version",
+    "--py-version", "--python-version", "--requires-python", metavar="python_version",
     dest="python_version", default=PYTHON_VERSION, type=str,
     help="required minor python version for the project"
 )
@@ -105,6 +156,11 @@ def add_to_parser(self, parser):
     help="do not synchronize the environment",
 )
 
+sync = Option(
+    "--sync", dest="sync", action="store_true", help="synchronize the environment",
+    default=False
+)
+
 target = Option(
     "-t", "--target", default=None,
     help="file to export into (default is to print to stdout)"
@@ -135,6 +191,10 @@ def add_to_parser(self, parser):
     help="do not remove packages not specified in Pipfile.lock",
 )
 
+clean = Option(
+    "--clean", dest="clean", action="store_true", default=False,
+    help="remove packages not specified in Pipfile.lock",
+)
 dev_only = Option(
     "--dev", dest="only", action="store_const", const="dev",
     help="only try to modify [dev-packages]",
@@ -152,5 +212,7 @@ def add_to_parser(self, parser):
 
 include_hashes_group = ArgumentGroup("include_hashes", is_mutually_exclusive=True, options=[include_hashes, no_include_hashes])
 dev_group = ArgumentGroup("dev", is_mutually_exclusive="True", options=[dev_only, default_only])
-package_group = ArgumentGroup("packages", options=[packages, editable, dev, no_sync])
 new_project_group = ArgumentGroup("new-project", options=[new_project, python_version])
+clean_group = ArgumentGroup("clean", is_mutually_exclusive=True, options=[clean, no_clean])
+sync_group = ArgumentGroup("sync", is_mutually_exclusive=True, options=[sync, no_sync])
+package_group = ArgumentGroup("packages", options=[packages, editable, dev, sync_group])
diff --git a/src/passa/cli/remove.py b/src/passa/cli/remove.py
index 538acbf..041c195 100644
--- a/src/passa/cli/remove.py
+++ b/src/passa/cli/remove.py
@@ -4,18 +4,18 @@
 
 from ..actions.remove import remove
 from ._base import BaseCommand
-from .options import dev_group, no_clean, packages
+from .options import dev_group, clean_group, sync_group, packages
 
 
 class Command(BaseCommand):
 
     name = "remove"
     description = "Remove packages from project."
-    arguments = [dev_group, no_clean, packages]
+    arguments = [dev_group, clean_group, sync_group, packages]
 
     def run(self, options):
         return remove(project=options.project, only=options.only,
-                        packages=options.packages, clean=options.clean)
+                        packages=options.packages, clean=options.clean, sync=options.sync)
 
 
 if __name__ == "__main__":
diff --git a/src/passa/cli/sync.py b/src/passa/cli/sync.py
index a09b784..9a31fe1 100644
--- a/src/passa/cli/sync.py
+++ b/src/passa/cli/sync.py
@@ -4,14 +4,14 @@
 
 from ..actions.sync import sync
 from ._base import BaseCommand
-from .options import dev, no_clean
+from .options import dev, clean_group
 
 
 class Command(BaseCommand):
 
     name = "sync"
     description = "Install Pipfile.lock into the environment."
-    arguments = [dev, no_clean]
+    arguments = [dev, clean_group]
 
     def run(self, options):
         return sync(project=options.project, dev=options.dev, clean=options.clean)
diff --git a/src/passa/cli/upgrade.py b/src/passa/cli/upgrade.py
index cf7f502..c7696c2 100644
--- a/src/passa/cli/upgrade.py
+++ b/src/passa/cli/upgrade.py
@@ -3,14 +3,14 @@
 
 from ..actions.upgrade import upgrade
 from ._base import BaseCommand
-from .options import no_clean, no_sync, packages, strategy
+from .options import clean_group, sync_group, packages, strategy
 
 
 class Command(BaseCommand):
 
     name = "upgrade"
     description = "Upgrade packages in project."
-    arguments = [packages, strategy, no_clean, no_sync]
+    arguments = [packages, strategy, clean_group, sync_group]
 
     def run(self, options):
         return upgrade(project=options.project, strategy=options.strategy,
diff --git a/src/passa/internals/_pip.py b/src/passa/internals/_pip.py
index 2aa143a..7b1a067 100644
--- a/src/passa/internals/_pip.py
+++ b/src/passa/internals/_pip.py
@@ -7,18 +7,24 @@
 import itertools
 import distutils.log
 import os
+import re
 
 import distlib.database
+import distlib.metadata
 import distlib.scripts
 import distlib.wheel
 import packaging.utils
 import pip_shims
-import setuptools.dist
 import six
+import sys
+import sysconfig
 import vistir
 
 from ..models.caches import CACHE_DIR
-from ._pip_shims import VCS_SUPPORT, build_wheel as _build_wheel, unpack_url
+from ..models.environments import Environment
+from ._pip_shims import (
+    SETUPTOOLS_SHIM, VCS_SUPPORT, build_wheel as _build_wheel, unpack_url
+)
 from .utils import filter_sources
 
 
@@ -87,21 +93,21 @@ def _get_pip_session(trusted_hosts):
     options, _ = cmd.parser.parse_args([])
     options.cache_dir = CACHE_DIR
     options.trusted_hosts = trusted_hosts
-    session = cmd._build_session(options)
-    return session
+    return cmd._build_session(options)
 
 
+@contextlib.contextmanager
 def _get_finder(sources):
     index_urls, trusted_hosts = _get_pip_index_urls(sources)
-    session = _get_pip_session(trusted_hosts)
-    finder = pip_shims.PackageFinder(
-        find_links=[],
-        index_urls=index_urls,
-        trusted_hosts=trusted_hosts,
-        allow_all_prereleases=True,
-        session=session,
-    )
-    return finder
+    with contextlib.closing(_get_pip_session(trusted_hosts)) as session:
+        finder = pip_shims.PackageFinder(
+            find_links=[],
+            index_urls=index_urls,
+            trusted_hosts=trusted_hosts,
+            allow_all_prereleases=True,
+            session=session,
+        )
+        yield finder
 
 
 def _get_wheel_cache():
@@ -134,7 +140,7 @@ class WheelBuildError(RuntimeError):
     pass
 
 
-def build_wheel(ireq, sources, hashes=None):
+def build_wheel(ireq, sources, finder, hashes=None):
     """Build a wheel file for the InstallRequirement object.
 
     An artifact is downloaded (or read from cache). If the artifact is not a
@@ -148,7 +154,6 @@ def build_wheel(ireq, sources, hashes=None):
     `RuntimeError` subclass) if the wheel cannot be built.
     """
     kwargs = _prepare_wheel_building_kwargs(ireq)
-    finder = _get_finder(sources)
 
     # Not for upgrade, hash not required. Hashes are not required here even
     # when we provide them, because pip skips local wheel cache if we set it
@@ -196,29 +201,15 @@ def build_wheel(ireq, sources, hashes=None):
     return distlib.wheel.Wheel(wheel_path)
 
 
-def _obtrain_ref(vcs_obj, src_dir, name, rev=None):
-    target_dir = os.path.join(src_dir, name)
-    target_rev = vcs_obj.make_rev_options(rev)
-    if not os.path.exists(target_dir):
-        vcs_obj.obtain(target_dir)
-    if (not vcs_obj.is_commit_id_equal(target_dir, rev) and
-            not vcs_obj.is_commit_id_equal(target_dir, target_rev)):
-        vcs_obj.update(target_dir, target_rev)
-    return vcs_obj.get_revision(target_dir)
-
-
 def get_vcs_ref(requirement):
-    backend = VCS_SUPPORT.get_backend(requirement.vcs)
-    vcs = backend(url=requirement.req.vcs_uri)
-    src = _get_src_dir()
-    name = requirement.normalized_name
-    ref = _obtrain_ref(vcs, src, name, rev=requirement.req.ref)
-    return ref
+    return requirement.commit_hash
 
 
 def find_installation_candidates(ireq, sources):
-    finder = _get_finder(sources)
-    return finder.find_all_candidates(ireq.name)
+    candidates = []
+    with _get_finder(sources) as finder:
+        candidates = finder.find_all_candidates(ireq.name)
+    return candidates
 
 
 class RequirementUninstaller(object):
@@ -227,17 +218,24 @@ class RequirementUninstaller(object):
     This uses `UninstallPathSet` to control the workflow. If the inner block
     exits correctly, the uninstallation is committed, otherwise rolled back.
     """
-    def __init__(self, ireq, auto_confirm, verbose):
+    def __init__(self, ireq, auto_confirm, verbose, env=None):
         self.ireq = ireq
         self.pathset = None
         self.auto_confirm = auto_confirm
         self.verbose = verbose
+        self.env = env if env else Environment()
+
+    def check_permitted(self, pathset, path):
+        if self.env.is_venv and self.env.is_installed(self.ireq.name):
+            return True
+        return pathset._permitted(path)
 
     def __enter__(self):
         self.pathset = self.ireq.uninstall(
             auto_confirm=self.auto_confirm,
             verbose=self.verbose,
         )
+        self.pathset._permitted = self.check_permitted
         return self.pathset
 
     def __exit__(self, exc_type, exc_value, traceback):
@@ -282,6 +280,7 @@ class NoopInstaller(object):
     arguments, and should be called in that order to prepare an installation
     operation, and to actually install things.
     """
+
     def prepare(self):
         pass
 
@@ -289,39 +288,172 @@ def install(self):
         pass
 
 
-class EditableInstaller(NoopInstaller):
-    """Installer to handle editable.
-    """
-    def __init__(self, requirement):
-        ireq = requirement.as_ireq()
-        self.working_directory = ireq.setup_py_dir
-        self.setup_py = ireq.setup_py
-
-    def install(self):
-        with vistir.cd(self.working_directory), _suppress_distutils_logs():
-            # Access from Setuptools to ensure things are patched correctly.
-            setuptools.dist.distutils.core.run_setup(
-                self.setup_py, ["develop", "--no-deps"],
-            )
-
+dist_info_re = re.compile(r"""^(?P<namever>(?P<name>.+?)(-(?P<ver>.+?))?)
+                                \.dist-info$""", re.VERBOSE)
 
-class WheelInstaller(NoopInstaller):
-    """Installer by building a wheel.
 
-    The wheel is built during `prepare()`, and installed in `install()`.
+def root_is_purelib(name, wheeldir):
     """
-    def __init__(self, requirement, sources, paths):
+    Return True if the extracted wheel in wheeldir should go into purelib.
+    """
+    name_folded = name.replace("-", "_")
+    for item in os.listdir(wheeldir):
+        match = dist_info_re.match(item)
+        if match and match.group('name') == name_folded:
+            with open(os.path.join(wheeldir, item, 'WHEEL')) as wheel:
+                for line in wheel:
+                    line = line.lower().rstrip()
+                    if line == "root-is-purelib: true":
+                        return True
+    return False
+
+
+def get_entrypoints(filename):
+    import pkg_resources
+    if not os.path.exists(filename):
+        return {}, {}
+
+    # This is done because you can pass a string to entry_points wrappers which
+    # means that they may or may not be valid INI files. The attempt here is to
+    # strip leading and trailing whitespace in order to make them valid INI
+    # files.
+    with open(filename) as fp:
+        data = io.StringIO()
+        for line in fp:
+            data.write(line.strip())
+            data.write("\n")
+        data.seek(0)
+
+    # get the entry points and then the script names
+    entry_points = pkg_resources.EntryPoint.parse_map(data)
+    console = entry_points.get('console_scripts', {})
+    gui = entry_points.get('gui_scripts', {})
+
+    def _split_ep(s):
+        """get the string representation of EntryPoint, remove space and split
+        on '='"""
+        return str(s).replace(" ", "").split("=")
+
+    # convert the EntryPoint objects into strings with module:function
+    console = dict(_split_ep(v) for v in console.values())
+    gui = dict(_split_ep(v) for v in gui.values())
+    return console, gui
+
+
+class BaseInstaller(NoopInstaller):
+    """Virtualenv-capable installer"""
+
+    def __init__(self, requirement, sources=None, environment=None):
         self.ireq = requirement.as_ireq()
         self.sources = filter_sources(requirement, sources)
         self.hashes = requirement.hashes or None
-        self.paths = paths
-        self.wheel = None
+        self.environment = environment if environment else Environment()
+        self.built = None
+        self.metadata = None
+        self.is_wheel = False
+
+    @property
+    def src_dir(self):
+        build_dir = os.environ.get("PASSA_BUILD_DIR", None)
+        if not build_dir:
+            build_dir = vistir.path.create_tracked_tempdir("passa-build-dir")
+        return build_dir
+
+    @property
+    def setup_dir(self):
+        if not self.built:
+            return self.ireq.setup_py_dir
+        return vistir.compat.Path(self.built.path).parent
+
+    @property
+    def installation_args(self):
+        install_arg = "install" if not self.ireq.editable else "develop"
+        setup_path = self.setup_dir.joinpath("setup.py")
+        install_keys = ["headers", "purelib", "platlib", "scripts", "data"]
+        install_args = [
+            self.environment.python, "-u", "-c", SETUPTOOLS_SHIM % setup_path.as_posix(),
+            install_arg, "--single-version-externally-managed", "--no-deps",
+            "--prefix={0}".format(self.environment.paths["prefix"])
+        ]
+        for key in install_keys:
+            install_args.append(
+                "--install-{0}={1}".format(key, self.environment.paths[key])
+            )
+        return install_args
+
+    def build_wheel(self):
+        with _get_finder(self.sources) as finder:
+            self.built = build_wheel(self.ireq, self.sources, finder, self.hashes)
+            self.metadata = self.built.metadata
+        self.is_wheel = True
+
+    def build_sdist(self):
+        with _get_finder(self.sources) as finder:
+            self.ireq.populate_link(finder, False, False)
+            self.ireq.ensure_has_source_dir(self.src_dir)
+            self.built = get_sdist(self.ireq)
+            self.metadata = read_sdist_metadata(self.ireq)
+
+    def install_wheel(self):
+        scripts = distlib.scripts.ScriptMaker(None, None)
+        self.built.install(self.environment.paths, scripts)
+
+    def install_sdist(self):
+        with vistir.cd(self.setup_dir.as_posix()), _suppress_distutils_logs():
+            c = self.environment.run(
+                self.installation_args, return_object=True, block=True, nospin=True,
+                combine_stderr=False, write_to_stdout=False
+            )
+            if c.returncode != 0:
+                err_text = "{0!r}: {1!r}".format(c.err, c.out)
+                raise RuntimeError("Failed to install package: {0!r}".format(err_text))
+            return
 
     def prepare(self):
-        self.wheel = build_wheel(self.ireq, self.sources, self.hashes)
+        pass
 
     def install(self):
-        self.wheel.install(self.paths, distlib.scripts.ScriptMaker(None, None))
+        with self.environment.activated():
+            self._install()
+
+
+class SdistInstaller(BaseInstaller):
+    """Installer for SDists"""
+    def __init__(self, *args, **kwargs):
+        super(SdistInstaller, self).__init__(*args, **kwargs)
+
+    def prepare(self):
+        try:
+            self.build_wheel()
+        except (WheelBuildError, distlib.metadata.MetadataConflictError):
+            self.build_sdist()
+            if not self.built or not self.metadata:
+                raise
+
+    def _install(self):
+        if self.is_wheel:
+            self.install_wheel()
+        else:
+            self.install_sdist()
+
+
+class Installer(SdistInstaller):
+    """Installer to handle editable.
+    """
+    def __init__(self, *args, **kwargs):
+        super(Installer, self).__init__(*args, **kwargs)
+
+    @property
+    def src_dir(self):
+        build_dir = os.environ.get("PIP_SRC", None)
+        venv = os.environ.get("VIRTUAL_ENV", None)
+        if venv:
+            src_dir = os.path.join(venv, "src")
+            if os.path.exists(src_dir):
+                build_dir = src_dir
+        if not build_dir:
+            build_dir = vistir.path.create_tracked_tempdir("passa-build-dir")
+        return build_dir
 
 
 def _iter_egg_info_directories(root, name):
@@ -389,9 +521,15 @@ def _find_egg_info(ireq):
     return top_egg_info
 
 
-def read_sdist_metadata(ireq):
+def get_sdist(ireq):
     egg_info_dir = _find_egg_info(ireq)
     if not egg_info_dir:
         return None
-    distribution = distlib.database.EggInfoDistribution(egg_info_dir)
-    return distribution.metadata
+    return distlib.database.EggInfoDistribution(egg_info_dir)
+
+
+def read_sdist_metadata(ireq):
+    sdist = get_sdist(ireq)
+    if not sdist:
+        return None
+    return sdist.metadata
diff --git a/src/passa/internals/_pip_shims.py b/src/passa/internals/_pip_shims.py
index b2c7b6e..87d0904 100644
--- a/src/passa/internals/_pip_shims.py
+++ b/src/passa/internals/_pip_shims.py
@@ -11,7 +11,19 @@
 
 from __future__ import absolute_import, unicode_literals
 
+import distlib.metadata
+import importlib
 import pip_shims
+import recursive_monkey_patch
+
+
+class LegacyMetadata(object):
+    def set_metadata_version(self):
+        metadata_version = self._fields.get("Metadata-Version")
+        if metadata_version == "2.1":
+            self._fields["Metadata-Version"] = metadata_version
+        else:
+            self._fields['Metadata-Version'] = distlib.metadata._best_version(self._fields)
 
 
 def _build_wheel_pre10(ireq, output_dir, finder, wheel_cache, kwargs):
@@ -47,8 +59,8 @@ def _unpack_url_pre10(*args, **kwargs):
     return pip_shims.unpack_url(*args, **kwargs)
 
 
-PIP_VERSION = pip_shims.utils._parse(pip_shims.pip_version)
-VERSION_10 = pip_shims.utils._parse("10")
+PIP_VERSION = pip_shims._parse(pip_shims.pip_version)
+VERSION_10 = pip_shims._parse("10")
 
 
 VCS_SUPPORT = pip_shims.VcsSupport()
@@ -59,3 +71,15 @@ def _unpack_url_pre10(*args, **kwargs):
 if PIP_VERSION < VERSION_10:
     build_wheel = _build_wheel_pre10
     unpack_url = _unpack_url_pre10
+
+
+SETUPTOOLS_SHIM = (
+    "import setuptools, tokenize;__file__=%r;"
+    "f=getattr(tokenize, 'open', open)(__file__);"
+    "code=f.read().replace('\\r\\n', '\\n');"
+    "f.close();"
+    "exec(compile(code, __file__, 'exec'))"
+)
+
+
+recursive_monkey_patch.monkey_patch(LegacyMetadata, distlib.metadata.LegacyMetadata)
diff --git a/src/passa/internals/dependencies.py b/src/passa/internals/dependencies.py
index 410a5e6..6c74b47 100644
--- a/src/passa/internals/dependencies.py
+++ b/src/passa/internals/dependencies.py
@@ -10,11 +10,12 @@
 import packaging.utils
 import packaging.version
 import requests
-import requirementslib
 import six
 
+import requirementslib
+
 from ..models.caches import DependencyCache, RequiresPythonCache
-from ._pip import WheelBuildError, build_wheel, read_sdist_metadata
+from ._pip import WheelBuildError, build_wheel, get_sdist, read_sdist_metadata
 from .markers import contains_extra, get_contained_extras, get_without_extra
 from .utils import get_pinned_version, is_pinned
 
@@ -140,20 +141,20 @@ def _get_dependencies_from_json(ireq, sources):
         if proc_url.endswith("/simple")
     ]
 
-    session = requests.session()
-
-    for prefix in url_prefixes:
-        url = "{prefix}/pypi/{name}/{version}/json".format(
-            prefix=prefix,
-            name=packaging.utils.canonicalize_name(ireq.name),
-            version=version,
-        )
-        try:
-            dependencies = _get_dependencies_from_json_url(url, session)
-            if dependencies is not None:
-                return dependencies
-        except Exception as e:
-            print("unable to read dependencies via {0} ({1})".format(url, e))
+    with requests.session() as session:
+
+        for prefix in url_prefixes:
+            url = "{prefix}/pypi/{name}/{version}/json".format(
+                prefix=prefix,
+                name=packaging.utils.canonicalize_name(ireq.name),
+                version=version,
+            )
+            try:
+                dependencies = _get_dependencies_from_json_url(url, session)
+                if dependencies is not None:
+                    return dependencies
+            except Exception as e:
+                print("unable to read dependencies via {0} ({1})".format(url, e))
     return
 
 
@@ -225,17 +226,18 @@ def _get_dependencies_from_pip(ireq, sources):
     """
     extras = ireq.extras or ()
     try:
-        wheel = build_wheel(ireq, sources)
+        built = build_wheel(ireq, sources)
     except WheelBuildError:
         # XXX: This depends on a side effect of `build_wheel`. This block is
         # reached when it fails to build an sdist, where the sdist would have
         # been downloaded, extracted into `ireq.source_dir`, and partially
         # built (hopefully containing .egg-info).
+        built = get_sdist(ireq)
         metadata = read_sdist_metadata(ireq)
         if not metadata:
             raise
     else:
-        metadata = wheel.metadata
+        metadata = built.metadata
     requirements = _read_requirements(metadata, extras)
     requires_python = _read_requires_python(metadata)
     return requirements, requires_python
diff --git a/src/passa/internals/utils.py b/src/passa/internals/utils.py
index 8f8e6fd..d9d6c0d 100644
--- a/src/passa/internals/utils.py
+++ b/src/passa/internals/utils.py
@@ -1,9 +1,33 @@
 # -*- coding=utf-8 -*-
 
-from __future__ import absolute_import, unicode_literals
+from __future__ import absolute_import, unicode_literals, print_function
+
+import atexit
+import os
+
+import requests
+
+
+def is_type_checking():
+    # type: () -> bool
+    try:
+        from typing import TYPE_CHECKING
+    except ImportError:
+        return False
+    return TYPE_CHECKING
+
+
+MYPY_RUNNING = os.environ.get("MYPY_RUNNING", is_type_checking())
+
+
+if MYPY_RUNNING:
+    from typing import Any, List, Dict  # noqa
+    from requirementslib.models.requirements import Requirement  # noqa
+    from pip_shims.shims import InstallRequirement  # noqa
 
 
 def identify_requirment(r):
+    # type: (Requirement) -> str
     """Produce an identifier for a requirement to use in the resolver.
 
     Note that we are treating the same package with different extras as
@@ -18,6 +42,7 @@ def identify_requirment(r):
 
 
 def get_pinned_version(ireq):
+    # type: (InstallRequirement) -> str
     """Get the pinned version of an InstallRequirement.
 
     An InstallRequirement is considered pinned if:
@@ -60,6 +85,7 @@ def get_pinned_version(ireq):
 
 
 def is_pinned(ireq):
+    # type: (InstallRequirement) -> bool
     """Returns whether an InstallRequirement is a "pinned" requirement.
 
     An InstallRequirement is considered pinned if:
@@ -83,6 +109,7 @@ def is_pinned(ireq):
 
 
 def filter_sources(requirement, sources):
+    # type: (Requirement, List[Dict[str, Union[bool, str]]]) -> List[Dict[str, Union[bool, str]]]
     """Returns a filtered list of sources for this requirement.
 
     This considers the index specified by the requirement, and returns only
@@ -98,11 +125,13 @@ def filter_sources(requirement, sources):
 
 
 def get_allow_prereleases(requirement, global_setting):
+    # type: (Requirement, bool) -> bool
     # TODO: Implement per-package prereleases flag. (pypa/pipenv#1696)
     return global_setting
 
 
 def are_requirements_equal(this, that):
+    # type: (Requirement, Requirement) -> bool
     return (
         this.as_line(include_hashes=False) ==
         that.as_line(include_hashes=False)
@@ -110,9 +139,22 @@ def are_requirements_equal(this, that):
 
 
 def strip_extras(requirement):
+    # type: (Requirement) -> Requirement
     """Returns a new requirement object with extras removed.
     """
     line = requirement.as_line()
     new = type(requirement).from_line(line)
     new.extras = None
     return new
+
+
+REQUESTS_SESSIONS = []  # type: List[requests.Session]
+
+
+def get_tracked_session():
+    # type: () -> requests.Session
+    """Build a requests session and register it to be closed with interpreter exit"""
+
+    session = requests.Session()
+    atexit.register(session.close)
+    return session
diff --git a/src/passa/models/caches.py b/src/passa/models/caches.py
index c6d29b5..ed8c92f 100644
--- a/src/passa/models/caches.py
+++ b/src/passa/models/caches.py
@@ -10,25 +10,33 @@
 
 import appdirs
 import pip_shims
-import requests
 import vistir
 
 from ..internals._pip_shims import VCS_SUPPORT
-from ..internals.utils import get_pinned_version
+from ..internals.utils import get_pinned_version, get_tracked_session, MYPY_RUNNING
 
 
-CACHE_DIR = os.environ.get("PASSA_CACHE_DIR", appdirs.user_cache_dir("passa"))
+if MYPY_RUNNING:
+    import requests  # noqa
+    from typing import Optional  # noqa
+
+
+CACHE_DIR = os.environ.get("PASSA_CACHE_DIR", appdirs.user_cache_dir("passa"))  # type: ignore
 
 
 class HashCache(pip_shims.SafeFileCache):
+
     """Caches hashes of PyPI artifacts so we do not need to re-download them.
 
     Hashes are only cached when the URL appears to contain a hash in it and the
     cache key includes the hash value returned from the server). This ought to
     avoid ssues where the location on the server changes.
     """
+
     def __init__(self, *args, **kwargs):
-        session = kwargs.pop('session', requests.session())
+        session = kwargs.pop('session', None)  # type: requests.Session
+        if session is None:
+            session = get_tracked_session()
         self.session = session
         kwargs.setdefault('directory', os.path.join(CACHE_DIR, 'hash-cache'))
         super(HashCache, self).__init__(*args, **kwargs)
@@ -76,6 +84,7 @@ def __str__(self):
 
 def _key_from_req(req):
     """Get an all-lowercase version of the requirement's name."""
+
     if hasattr(req, 'key'):
         # from pkg_resources, such as installed dists for pip-sync
         key = req.key
@@ -100,6 +109,7 @@ def _read_cache_file(cache_file_path):
 
 
 class _JSONCache(object):
+
     """A persistent cache backed by a JSON file.
 
     The cache file is written to the appropriate user cache dir for the
@@ -109,7 +119,8 @@ class _JSONCache(object):
 
     Where X.Y indicates the Python version.
     """
-    filename_format = None
+
+    filename_format = None  # type: Optional[str]
 
     def __init__(self, cache_dir=CACHE_DIR):
         vistir.mkdir_p(cache_dir)
@@ -122,10 +133,12 @@ def __init__(self, cache_dir=CACHE_DIR):
 
     @property
     def cache(self):
-        """The dictionary that is the actual in-memory cache.
+        """
+        The dictionary that is the actual in-memory cache.
 
         This property lazily loads the cache from disk.
         """
+
         if self._cache is None:
             self.read_cache()
         return self._cache
@@ -144,6 +157,7 @@ def as_cache_key(self, ireq):
 
             ("ipython", "2.1.0[nbconvert,notebook]")
         """
+
         extras = tuple(sorted(ireq.extras))
         if not extras:
             extras_string = ""
@@ -154,16 +168,16 @@ def as_cache_key(self, ireq):
         return name, "{}{}".format(version, extras_string)
 
     def read_cache(self):
-        """Reads the cached contents into memory.
-        """
+        """Reads the cached contents into memory."""
+
         if os.path.exists(self._cache_file):
             self._cache = _read_cache_file(self._cache_file)
         else:
             self._cache = {}
 
     def write_cache(self):
-        """Writes the cache to disk as JSON.
-        """
+        """Writes the cache to disk as JSON."""
+
         doc = {
             '__format__': 1,
             'dependencies': self._cache,
@@ -203,12 +217,18 @@ def get(self, ireq, default=None):
 
 
 class DependencyCache(_JSONCache):
-    """Cache the dependency of cancidates.
+
     """
+    Cache the dependency of cancidates.
+    """
+
     filename_format = "depcache-py{python_version}.json"
 
 
 class RequiresPythonCache(_JSONCache):
-    """Cache a candidate's Requires-Python information.
+
     """
+    Cache a candidate's Requires-Python information.
+    """
+
     filename_format = "pyreqcache-py{python_version}.json"
diff --git a/src/passa/models/environments.py b/src/passa/models/environments.py
new file mode 100644
index 0000000..bb52d13
--- /dev/null
+++ b/src/passa/models/environments.py
@@ -0,0 +1,452 @@
+# -*- coding=utf-8 -*-
+
+import contextlib
+import importlib
+import json
+import os
+import site
+import sys
+
+from distutils.sysconfig import get_python_lib
+from functools import partial
+from sysconfig import get_paths
+
+import pkg_resources
+import six
+
+from cached_property import cached_property
+
+import vistir
+
+
+BASE_WORKING_SET = pkg_resources.WorkingSet(sys.path)
+run = partial(vistir.misc.run, write_to_stdout=False, nospin=True, block=True)
+
+
+class Environment(object):
+    def __init__(self, prefix=None, is_venv=False, base_working_set=None):
+        self.base_working_set = base_working_set if base_working_set else BASE_WORKING_SET
+        self._modules = {'pkg_resources': pkg_resources}
+        self.extra_dists = []
+        prefix = prefix if prefix else sys.prefix
+        prefix = vistir.path.normalize_path(prefix)
+        sys_prefix = vistir.path.normalize_path(sys.prefix)
+        prefix = prefix if prefix else sys_prefix
+        self.is_venv = is_venv or prefix != sys_prefix
+        self.prefix = vistir.compat.Path(prefix)
+        self.sys_paths = get_paths()
+        super(Environment, self).__init__()
+
+    def safe_import(self, name):
+        """Helper utility for reimporting previously imported modules while inside the env"""
+        module = None
+        if name not in self._modules:
+            self._modules[name] = importlib.import_module(name)
+        module = self._modules[name]
+        if not module:
+            dist = next(iter(
+                dist for dist in self.base_working_set if dist.project_name == name
+            ), None)
+            if dist:
+                dist.activate()
+            module = importlib.import_module(name)
+        if name in sys.modules:
+            try:
+                six.moves.reload_module(module)
+                six.moves.reload_module(sys.modules[name])
+            except TypeError:
+                del sys.modules[name]
+                sys.modules[name] = self._modules[name]
+        return module
+
+    @classmethod
+    def resolve_dist(cls, dist, working_set):
+        """Given a local distribution and a working set, returns all dependencies from the set.
+
+        :param dist: A single distribution to find the dependencies of
+        :type dist: :class:`pkg_resources.Distribution`
+        :param working_set: A working set to search for all packages
+        :type working_set: :class:`pkg_resources.WorkingSet`
+        :return: A set of distributions which the package depends on, including the package
+        :rtype: set(:class:`pkg_resources.Distribution`)
+        """
+
+        deps = set()
+        deps.add(dist)
+        try:
+            reqs = dist.requires()
+        except (AttributeError, OSError, IOError):  # The METADATA file can't be found
+            return deps
+        for req in reqs:
+            dist = working_set.find(req)
+            deps |= cls.resolve_dist(dist, working_set)
+        return deps
+
+    def add_dist(self, dist_name):
+        dist = pkg_resources.get_distribution(pkg_resources.Requirement(dist_name))
+        extras = self.resolve_dist(dist, self.base_working_set)
+        if extras:
+            self.extra_dists.extend(extras)
+
+    @cached_property
+    def python_version(self):
+        with self.activated():
+            sysconfig = self.safe_import("sysconfig")
+            py_version = sysconfig.get_python_version()
+            return py_version
+
+    @property
+    def python_info(self):
+        include_dir = self.prefix / "include"
+        python_path = next(iter(list(include_dir.iterdir())), None)
+        if python_path and python_path.name.startswith("python"):
+            python_version = python_path.name.replace("python", "")
+            py_version_short, abiflags = python_version[:3], python_version[3:]
+            return {"py_version_short": py_version_short, "abiflags": abiflags}
+        return {}
+
+    @cached_property
+    def base_paths(self):
+        """
+        Returns the context appropriate paths for the environment.
+
+        :return: A dictionary of environment specific paths to be used for installation operations
+        :rtype: dict
+
+        .. note:: The implementation of this is borrowed from a combination of pip and
+           virtualenv and is likely to change at some point in the future.
+
+        >>> from pipenv.core import project
+        >>> from pipenv.environment import Environment
+        >>> env = Environment(prefix=project.virtualenv_location, is_venv=True, sources=project.sources)
+        >>> import pprint
+        >>> pprint.pprint(env.base_paths)
+        {'PATH': '/home/hawk/.virtualenvs/pipenv-MfOPs1lW/bin::/bin:/usr/bin',
+        'PYTHONPATH': '/home/hawk/.virtualenvs/pipenv-MfOPs1lW/lib/python3.7/site-packages',
+        'data': '/home/hawk/.virtualenvs/pipenv-MfOPs1lW',
+        'include': '/home/hawk/.pyenv/versions/3.7.1/include/python3.7m',
+        'libdir': '/home/hawk/.virtualenvs/pipenv-MfOPs1lW/lib/python3.7/site-packages',
+        'platinclude': '/home/hawk/.pyenv/versions/3.7.1/include/python3.7m',
+        'platlib': '/home/hawk/.virtualenvs/pipenv-MfOPs1lW/lib/python3.7/site-packages',
+        'platstdlib': '/home/hawk/.virtualenvs/pipenv-MfOPs1lW/lib/python3.7',
+        'prefix': '/home/hawk/.virtualenvs/pipenv-MfOPs1lW',
+        'purelib': '/home/hawk/.virtualenvs/pipenv-MfOPs1lW/lib/python3.7/site-packages',
+        'scripts': '/home/hawk/.virtualenvs/pipenv-MfOPs1lW/bin',
+        'stdlib': '/home/hawk/.pyenv/versions/3.7.1/lib/python3.7'}
+        """
+
+        prefix = self.prefix.as_posix()
+        install_scheme = 'nt' if (os.name == 'nt') else 'posix_prefix'
+        paths = get_paths(install_scheme, vars={
+            'base': prefix,
+            'platbase': prefix,
+        })
+        paths["PATH"] = paths["scripts"] + os.pathsep + os.defpath
+        if "prefix" not in paths:
+            paths["prefix"] = prefix
+        purelib = get_python_lib(plat_specific=0, prefix=prefix)
+        platlib = get_python_lib(plat_specific=1, prefix=prefix)
+        if purelib == platlib:
+            lib_dirs = purelib
+        else:
+            lib_dirs = purelib + os.pathsep + platlib
+        paths["libdir"] = purelib
+        paths["purelib"] = purelib
+        paths["platlib"] = platlib
+        paths['PYTHONPATH'] = lib_dirs
+        paths["libdirs"] = lib_dirs
+        return paths
+
+    @cached_property
+    def script_basedir(self):
+        """Path to the environment scripts dir"""
+        script_dir = self.base_paths["scripts"]
+        return script_dir
+
+    @property
+    def python(self):
+        """Path to the environment python"""
+        py = vistir.compat.Path(self.base_paths["scripts"]).joinpath("python").as_posix()
+        if not py:
+            return vistir.compat.Path(sys.executable).as_posix()
+        return py
+
+    @cached_property
+    def sys_path(self):
+        """
+        The system path inside the environment
+
+        :return: The :data:`sys.path` from the environment
+        :rtype: list
+        """
+
+        current_executable = vistir.compat.Path(sys.executable).as_posix()
+        if not self.python or self.python == current_executable:
+            return sys.path
+        elif any([sys.prefix == self.prefix, not self.is_venv]):
+            return sys.path
+        cmd_args = [self.python, "-c", "import json, sys; print(json.dumps(sys.path))"]
+        path, _ = run(cmd_args, return_object=False, combine_stderr=False)
+        path = json.loads(path.strip())
+        return path
+
+    @cached_property
+    def sys_prefix(self):
+        """
+        The prefix run inside the context of the environment
+
+        :return: The python prefix inside the environment
+        :rtype: :data:`sys.prefix`
+        """
+
+        command = [self.python, "-c" "import sys; print(sys.prefix)"]
+        c = run(command, return_object=True)
+        sys_prefix = vistir.compat.Path(vistir.misc.to_text(c.out).strip()).as_posix()
+        return sys_prefix
+
+    @property
+    def scripts_dir(self):
+        return self.paths["scripts"]
+
+    @property
+    def libdir(self):
+        purelib = self.paths.get("purelib", None)
+        if purelib and os.path.exists(purelib):
+            return "purelib", purelib
+        return "platlib", self.paths["platlib"]
+
+    @cached_property
+    def paths(self):
+        paths = {}
+        with vistir.contextmanagers.temp_environ(), vistir.contextmanagers.temp_path():
+            os.environ["PYTHONIOENCODING"] = vistir.compat.fs_str("utf-8")
+            os.environ["PYTHONDONTWRITEBYTECODE"] = vistir.compat.fs_str("1")
+            paths = self.base_paths
+            os.environ["PATH"] = paths["PATH"]
+            os.environ["PYTHONPATH"] = paths["PYTHONPATH"]
+            if "headers" not in paths:
+                paths["headers"] = paths["include"]
+        return paths
+
+    def get_distributions(self):
+        """Retrives the distributions installed on the library path of the environment
+
+        :return: A set of distributions found on the library path
+        :rtype: iterator
+        """
+
+        pkg_resources = self.safe_import("pkg_resources")
+        return pkg_resources.find_distributions(self.paths["PYTHONPATH"], only=True)
+
+    def find_egg(self, egg_dist):
+        """Find an egg by name in the given environment"""
+
+        site_packages = self.libdir[1]
+        search_filename = "{0}.egg-link".format(egg_dist.project_name)
+        try:
+            user_site = site.getusersitepackages()
+        except AttributeError:
+            user_site = site.USER_SITE
+        search_locations = [site_packages, user_site]
+        for site_directory in search_locations:
+            egg = os.path.join(site_directory, search_filename)
+            if os.path.isfile(egg):
+                return egg
+
+    def locate_dist(self, dist):
+        """
+        Given a distribution, try to find a corresponding egg link first.
+
+        If the egg - link doesn 't exist, return the supplied distribution."""
+
+        location = self.find_egg(dist)
+        return location or dist.location
+
+    def dist_is_in_project(self, dist):
+        """Determine whether the supplied distribution is in the environment."""
+
+        prefix = vistir.path.normalize_path(self.base_paths["prefix"])
+        location = self.locate_dist(dist)
+        if not location:
+            return False
+        return vistir.path.normalize_path(location).startswith(prefix)
+
+    def get_installed_packages(self):
+        """
+        Returns all of the installed packages in a given environment"""
+
+        workingset = self.get_working_set()
+        packages = [pkg for pkg in workingset if self.dist_is_in_project(pkg)]
+        return packages
+
+    def get_working_set(self):
+        """Retrieve the working set of installed packages for the environment.
+
+        :return: The working set for the environment
+        :rtype: :class:`pkg_resources.WorkingSet`
+        """
+
+        working_set = None
+        import pkg_resources
+        working_set = pkg_resources.WorkingSet(self.sys_path)
+        return working_set
+
+    def is_installed(self, pkgname):
+        """Given a package name, returns whether it is installed in the environment
+
+        :param str pkgname: The name of a package
+        :return: Whether the supplied package is installed in the environment
+        :rtype: bool
+        """
+
+        return any(d for d in self.get_distributions() if d.project_name == pkgname)
+
+    def run(self, cmd, cwd=os.curdir):
+        """Run a command with :class:`~subprocess.Popen` in the context of the environment
+
+        :param cmd: A command to run in the environment
+        :type cmd: str or list
+        :param str cwd: The working directory in which to execute the command, defaults to :data:`os.curdir`
+        :return: A finished command object
+        :rtype: :class:`~subprocess.Popen`
+        """
+
+        c = None
+        with self.activated():
+            script = vistir.cmdparse.Script.parse(cmd)
+            c = run(script._parts, return_object=True, cwd=cwd)
+        return c
+
+    def run_py(self, cmd, cwd=os.curdir):
+        """Run a python command in the enviornment context.
+
+        :param cmd: A command to run in the environment - runs with `python -c`
+        :type cmd: str or list
+        :param str cwd: The working directory in which to execute the command, defaults to :data:`os.curdir`
+        :return: A finished command object
+        :rtype: :class:`~subprocess.Popen`
+        """
+
+        c = None
+        if isinstance(cmd, six.string_types):
+            script = vistir.cmdparse.Script.parse("{0} -c {1}".format(self.python, cmd))
+        else:
+            script = vistir.cmdparse.Script.parse([self.python, "-c"] + list(cmd))
+        with self.activated():
+            c = run(script._parts, return_object=True, cwd=cwd)
+        return c
+
+    def run_activate_this(self):
+        """Runs the environment's inline activation script"""
+        if self.is_venv:
+            activate_this = os.path.join(self.scripts_dir, "activate_this.py")
+            if not os.path.isfile(activate_this):
+                raise OSError("No such file: {0!s}".format(activate_this))
+            with open(activate_this, "r") as f:
+                code = compile(f.read(), activate_this, "exec")
+                exec(code, dict(__file__=activate_this))
+
+    @contextlib.contextmanager
+    def activated(self, include_extras=True, extra_dists=None):
+        """Helper context manager to activate the environment.
+
+        This context manager will set the following variables for the duration
+        of its activation:
+
+            * sys.prefix
+            * sys.path
+            * os.environ["VIRTUAL_ENV"]
+            * os.environ["PATH"]
+
+        In addition, it will make any distributions passed into `extra_dists` available
+        on `sys.path` while inside the context manager, as well as making `passa` itself
+        available.
+
+        The environment's `prefix` as well as `scripts_dir` properties are both prepended
+        to `os.environ["PATH"]` to ensure that calls to `~Environment.run()` use the
+        environment's path preferentially.
+        """
+
+        if not extra_dists:
+            extra_dists = []
+        original_prefix = sys.prefix
+        parent_path = vistir.compat.Path(__file__).absolute().parent.parent.as_posix()
+        prefix = self.prefix.as_posix()
+        with vistir.contextmanagers.temp_environ(), vistir.contextmanagers.temp_path():
+            os.environ["PATH"] = os.pathsep.join([
+                vistir.compat.fs_str(self.scripts_dir),
+                vistir.compat.fs_str(self.prefix.as_posix()),
+                os.environ.get("PATH", os.defpath)
+            ])
+            os.environ["PYTHONIOENCODING"] = vistir.compat.fs_str("utf-8")
+            os.environ["PYTHONDONTWRITEBYTECODE"] = vistir.compat.fs_str("1")
+            os.environ["PYTHONPATH"] = self.base_paths["PYTHONPATH"]
+            if self.is_venv:
+                os.environ["VIRTUAL_ENV"] = vistir.compat.fs_str(prefix)
+            sys.path = self.sys_path
+            sys.prefix = self.sys_prefix
+            pkg_resources = self.safe_import("pkg_resources")
+            site = self.safe_import("site")
+            site.addsitedir(self.libdir[1])
+            if include_extras:
+                site.addsitedir(parent_path)
+                extra_dists = list(self.extra_dists) + extra_dists
+                for extra_dist in extra_dists:
+                    if extra_dist not in self.get_working_set():
+                        extra_dist.activate(self.sys_path)
+            try:
+                yield
+            finally:
+                sys.prefix = original_prefix
+                six.moves.reload_module(pkg_resources)
+
+    @contextlib.contextmanager
+    def uninstall(self, pkgname, *args, **kwargs):
+        """A context manager which allows uninstallation of packages from the environment
+
+        :param str pkgname: The name of a package to uninstall
+
+        >>> env = Environment("/path/to/env/root")
+        >>> with env.uninstall("pytz", auto_confirm=True, verbose=False) as uninstaller:
+                cleaned = uninstaller.paths
+        >>> if cleaned:
+                print("uninstalled packages: %s" % cleaned)
+        """
+
+        auto_confirm = kwargs.pop("auto_confirm", True)
+        verbose = kwargs.pop("verbose", False)
+        with self.activated():
+            monkey_patch = next(iter(
+                dist for dist in self.base_working_set
+                if dist.project_name == "recursive-monkey-patch"
+            ), None)
+            if monkey_patch:
+                monkey_patch.activate()
+            pip_shims = self.safe_import("pip_shims")
+            pathset_base = pip_shims.UninstallPathSet
+            import recursive_monkey_patch
+            recursive_monkey_patch.monkey_patch(
+                PatchedUninstaller, pathset_base
+            )
+            dist = next(
+                iter(filter(lambda d: d.project_name == pkgname, self.get_working_set())),
+                None
+            )
+            pathset = pathset_base.from_dist(dist)
+            if pathset is not None:
+                pathset.remove(auto_confirm=auto_confirm, verbose=verbose)
+            try:
+                yield pathset
+            except Exception as e:
+                if pathset is not None:
+                    pathset.rollback()
+            else:
+                if pathset is not None:
+                    pathset.commit()
+            if pathset is None:
+                return
+
+
+class PatchedUninstaller(object):
+    def _permitted(self, path):
+        return True
diff --git a/src/passa/models/projects.py b/src/passa/models/projects.py
index f6e037d..5c8d027 100644
--- a/src/passa/models/projects.py
+++ b/src/passa/models/projects.py
@@ -14,6 +14,8 @@
 import six
 import tomlkit
 
+from .environments import Environment
+
 
 SectionDifference = collections.namedtuple("SectionDifference", [
     "inthis", "inthat",
@@ -84,6 +86,7 @@ def dumps(self):
 class Project(object):
 
     root = attr.ib()
+    environment = attr.ib(default=attr.Factory(Environment))
     _p = attr.ib(init=False)
     _l = attr.ib(init=False)
 
diff --git a/src/passa/models/synchronizers.py b/src/passa/models/synchronizers.py
index bad4905..1ba8fa6 100644
--- a/src/passa/models/synchronizers.py
+++ b/src/passa/models/synchronizers.py
@@ -1,6 +1,6 @@
 # -*- coding=utf-8 -*-
 
-from __future__ import absolute_import, unicode_literals
+from __future__ import absolute_import, unicode_literals, print_function
 
 import collections
 import contextlib
@@ -8,21 +8,24 @@
 import sys
 import sysconfig
 
+import distlib.wheel
 import pkg_resources
 
 import packaging.markers
 import packaging.version
 import requirementslib
 
-from ..internals._pip import uninstall, EditableInstaller, WheelInstaller
+from ..internals._pip import uninstall, Installer
 
 
-def _is_installation_local(name):
+def _is_installation_local(name, environment=None):
     """Check whether the distribution is in the current Python installation.
 
-    This is used to distinguish packages seen by a virtual environment. A venv
+    This is used to distinguish packages seen by a virtual environment. A environment
     may be able to see global packages, but we don't want to mess with them.
     """
+    if environment:
+        return environment.is_installed(name)
     loc = os.path.normcase(pkg_resources.working_set.by_key[name].location)
     pre = os.path.normcase(sys.prefix)
     return os.path.commonprefix([loc, pre]) == pre
@@ -38,12 +41,14 @@ def _is_up_to_date(distro, version):
 ])
 
 
-def _group_installed_names(packages):
+def _group_installed_names(packages, environment=None):
     """Group locally installed packages based on given specifications.
 
     `packages` is a name-package mapping that are used as baseline to
     determine how the installed package should be grouped.
 
+    `environment` is the virtual environment object of the virtualenv being installed into.
+
     Returns a 3-tuple of disjoint sets, all containing names of installed
     packages:
 
@@ -54,8 +59,13 @@ def _group_installed_names(packages):
     """
     groupcoll = GroupCollection(set(), set(), set(), set())
 
-    for distro in pkg_resources.working_set:
-        name = distro.key
+    if environment:
+        working_set = environment.get_working_set()
+    else:
+        working_set = pkg_resources.working_set
+
+    for dist in working_set:
+        name = dist.key
         try:
             package = packages[name]
         except KeyError:
@@ -66,7 +76,7 @@ def _group_installed_names(packages):
         if not r.is_named:
             # Always mark non-named. I think pip does something similar?
             groupcoll.outdated.add(name)
-        elif not _is_up_to_date(distro, r.get_version()):
+        elif not _is_up_to_date(dist, r.get_version()):
             groupcoll.outdated.add(name)
         else:
             groupcoll.uptodate.add(name)
@@ -75,11 +85,14 @@ def _group_installed_names(packages):
 
 
 @contextlib.contextmanager
-def _remove_package(name):
-    if name is None or not _is_installation_local(name):
+def _remove_package(name, environment=None):
+    if name is None or not _is_installation_local(name, environment=environment):
         yield None
         return
-    with uninstall(name, auto_confirm=True, verbose=False) as uninstaller:
+    _uninstall = uninstall
+    if environment:
+        _uninstall = environment.uninstall
+    with _uninstall(name, auto_confirm=True, verbose=False) as uninstaller:
         yield uninstaller
 
 
@@ -88,19 +101,22 @@ def _get_packages(lockfile, default, develop):
     # Extras don't matter because they only affect dependencies, and we
     # don't install dependencies anyway!
     packages = {}
-    if default:
-        packages.update(lockfile.default._data)
     if develop:
         packages.update(lockfile.develop._data)
+    if default:
+        packages.update(lockfile.default._data)
     return packages
 
 
-def _build_paths():
+def _build_paths(environment=None):
     """Prepare paths for distlib.wheel.Wheel to install into.
     """
-    paths = sysconfig.get_paths()
+    if environment:
+        paths = environment.paths
+    else:
+        paths = sysconfig.get_paths()
     return {
-        "prefix": sys.prefix,
+        "prefix": sys.prefix if not environment else environment.prefix.as_posix(),
         "data": paths["data"],
         "scripts": paths["scripts"],
         "headers": paths["include"],
@@ -112,12 +128,12 @@ def _build_paths():
 PROTECTED_FROM_CLEAN = {"setuptools", "pip", "wheel"}
 
 
-def _clean(names):
+def _clean(names, environment=None):
     cleaned = set()
     for name in names:
         if name in PROTECTED_FROM_CLEAN:
             continue
-        with _remove_package(name) as uninst:
+        with _remove_package(name, environment=environment) as uninst:
             if uninst:
                 cleaned.add(name)
     return cleaned
@@ -126,18 +142,36 @@ def _clean(names):
 class Synchronizer(object):
     """Helper class to install packages from a project's lock file.
     """
-    def __init__(self, project, default, develop, clean_unneeded):
+    def __init__(self, project, default, develop, clean_unneeded, environment=None):
         self._root = project.root   # Only for repr.
+        self.project = project
         self.packages = _get_packages(project.lockfile, default, develop)
         self.sources = project.lockfile.meta.sources._data
-        self.paths = _build_paths()
         self.clean_unneeded = clean_unneeded
+        if not environment:
+            self._environment = getattr(project, "environment", None)
+        else:
+            self._environment = environment
+        super(Synchronizer, self).__init__()
+        self.paths = _build_paths(environment=self.environment)
+
+    @property
+    def environment(self):
+        if self._environment:
+            return self._environment
+        return self.project.environment
 
     def __repr__(self):
         return "<{0} @ {1!r}>".format(type(self).__name__, self._root)
 
     def sync(self):
-        groupcoll = _group_installed_names(self.packages)
+        if not self.environment:
+            return self._sync()
+        with self.environment.activated():
+            return self._sync()
+
+    def _sync(self):
+        groupcoll = _group_installed_names(self.packages, environment=self.environment)
 
         installed = set()
         updated = set()
@@ -146,7 +180,7 @@ def sync(self):
         # TODO: Show a prompt to confirm cleaning. We will need to implement a
         # reporter pattern for this as well.
         if self.clean_unneeded:
-            names = _clean(groupcoll.unneeded)
+            names = _clean(groupcoll.unneeded, environment=self.environment)
             cleaned.update(names)
 
         # TODO: Specify installation order? (pypa/pipenv#2274)
@@ -160,10 +194,7 @@ def sync(self):
             if markers and not packaging.markers.Marker(markers).evaluate():
                 continue
             r.markers = None
-            if r.editable:
-                installer = EditableInstaller(r)
-            else:
-                installer = WheelInstaller(r, self.sources, self.paths)
+            installer = Installer(r, sources=self.sources, environment=self.environment)
             try:
                 installer.prepare()
             except Exception as e:
@@ -181,7 +212,7 @@ def sync(self):
             else:
                 name_to_remove = None
             try:
-                with _remove_package(name_to_remove):
+                with _remove_package(name_to_remove, environment=self.environment):
                     installer.install()
             except Exception as e:
                 if os.environ.get("PASSA_NO_SUPPRESS_EXCEPTIONS"):
@@ -201,14 +232,27 @@ def sync(self):
 class Cleaner(object):
     """Helper class to clean packages not in a project's lock file.
     """
-    def __init__(self, project, default, develop):
+    def __init__(self, project, default, develop, sync=True, verbose=False):
         self._root = project.root   # Only for repr.
         self.packages = _get_packages(project.lockfile, default, develop)
+        self.sync = sync
+        self.project = project
 
     def __repr__(self):
         return "<{0} @ {1!r}>".format(type(self).__name__, self._root)
 
+    def print(self, packages):
+        if not self.sync:
+            message = "Would clean: {0}"
+        else:
+            message = "Cleaned: {0}"
+        print(message.format(", ".join(sorted(set(packages)))))
+
     def clean(self):
-        groupcoll = _group_installed_names(self.packages)
-        cleaned = _clean(groupcoll.unneeded)
+        groupcoll = _group_installed_names(self.packages, environment=self.project.environment)
+        cleaned = set()
+        if self.sync:
+            cleaned = _clean(groupcoll.unneeded, environment=self.project.environment)
+        else:
+            return groupcoll.unneeded
         return cleaned
diff --git a/src/passa/operations/sync.py b/src/passa/operations/sync.py
index 3014e8d..45502a4 100644
--- a/src/passa/operations/sync.py
+++ b/src/passa/operations/sync.py
@@ -16,8 +16,8 @@ def sync(syncer):
 
 
 def clean(cleaner):
-    print("Cleaning")
+    print("Cleaning...")
     cleaned = cleaner.clean()
     if cleaned:
-        print("Uninstalled: {}".format(", ".join(sorted(cleaned))))
+        cleaner.print(cleaned)
     return True
diff --git a/tasks/admin.py b/tasks/admin.py
index 2fabe99..fa1be74 100644
--- a/tasks/admin.py
+++ b/tasks/admin.py
@@ -14,6 +14,14 @@
 INIT_PY = ROOT.joinpath('src', PACKAGE_NAME, '__init__.py')
 
 
+@invoke.task()
+def typecheck(ctx):
+    src_dir = ROOT / "src" / PACKAGE_NAME
+    src_dir = src_dir.as_posix()
+    env = {"MYPYPATH": src_dir}
+    ctx.run(f"mypy {src_dir}", env=env)
+
+
 @invoke.task()
 def clean(ctx):
     """Clean previously built package artifacts.
diff --git a/tasks/package.py b/tasks/package.py
index f229e3a..bba878b 100644
--- a/tasks/package.py
+++ b/tasks/package.py
@@ -22,7 +22,6 @@
 
     'importlib',    # We only support 2.7 so this is not needed.
     'modutil',      # This breaks <3.7.
-    'toml',         # Why is requirementslib still not dropping it?
     'typing',       # This breaks 2.7. We'll provide a special stub for it.
 }
 
diff --git a/tests/actions/__init__.py b/tests/actions/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/actions/test_add.py b/tests/actions/test_add.py
new file mode 100644
index 0000000..e7cd883
--- /dev/null
+++ b/tests/actions/test_add.py
@@ -0,0 +1,20 @@
+# -*- coding=utf-8 -*-
+import passa.actions.init
+import passa.actions.add
+import passa.cli.options
+import passa.models.projects
+
+
+def test_add_one(project_directory):
+    project = passa.cli.options.Project(project_directory.strpath)
+    retcode = passa.actions.add.add_packages(["pytz"], project=project)
+    assert not retcode
+    assert 'pytz' in project.lockfile.default
+
+
+def test_add_one_with_deps(project_directory):
+    project = passa.cli.options.Project(project_directory.strpath)
+    retcode = passa.actions.add.add_packages(["requests"], project=project)
+    assert not retcode
+    assert 'requests' in project.lockfile.default
+    assert 'idna' in project.lockfile.default
diff --git a/tests/actions/test_clean.py b/tests/actions/test_clean.py
new file mode 100644
index 0000000..68562f9
--- /dev/null
+++ b/tests/actions/test_clean.py
@@ -0,0 +1,20 @@
+# -*- coding=utf-8 -*-
+import passa.actions.add
+import passa.actions.clean
+
+
+def test_clean(project):
+    retcode = passa.actions.add.add_packages(["requests"], project=project)
+    assert not retcode
+    packages = ["requests", "chardet", "certifi", "idna"]
+    c = project.env.run("pip install pytz")
+    assert c.returncode == 0
+    assert project.env.is_installed("pytz")
+    c = project.env.run("python -c 'import pytz'")
+    assert c.returncode == 0
+    clean_retcode = passa.actions.clean.clean(project=project)
+    assert not clean_retcode
+    assert not project.env.is_installed("pytz")
+    c = project.env.run("python -c 'import pytz'")
+    assert c.returncode != 0
+    assert all(pkg in project.lockfile.default for pkg in packages)
diff --git a/tests/actions/test_freeze.py b/tests/actions/test_freeze.py
new file mode 100644
index 0000000..53d34f9
--- /dev/null
+++ b/tests/actions/test_freeze.py
@@ -0,0 +1,21 @@
+# -*- coding=utf-8 -*-
+import passa.actions.add
+import passa.actions.freeze
+import passa.cli.options
+import passa.models.projects
+
+
+def test_freeze(project_directory):
+    project = passa.cli.options.Project(project_directory.strpath)
+    retcode = passa.actions.add.add_packages(["requests"], project=project)
+    assert not retcode
+    packages = ["requests", "chardet", "certifi", "idna"]
+    assert all(pkg in project.lockfile.default for pkg in packages)
+    freeze_file = project_directory.join("requirements.txt")
+    freeze_retcode = passa.actions.freeze.freeze(
+        project=project, include_hashes=False, target=freeze_file.strpath
+    )
+    assert not freeze_retcode
+    lines = [line.strip() for line in freeze_file.readlines() if line.strip() != '']
+    for pkg in packages:
+        assert any(line.startswith(pkg) for line in lines)
diff --git a/tests/actions/test_init.py b/tests/actions/test_init.py
new file mode 100644
index 0000000..2f12530
--- /dev/null
+++ b/tests/actions/test_init.py
@@ -0,0 +1,19 @@
+# -*- coding=utf-8 -*-
+
+import pytest
+
+import passa.actions.init
+import passa.cli.options
+
+
+def test_init(tmpdir):
+    init_retcode = passa.actions.init.init_project(root=tmpdir.strpath)
+    assert init_retcode == 0
+    project = passa.cli.options.Project(tmpdir.strpath)
+    assert project.pipfile.packages._data == {}
+    assert project.pipfile.dev_packages._data == {}
+
+
+def test_init_exists(project_directory):
+    with pytest.raises(RuntimeError, match=r'.* is already a Pipfile project'):
+        passa.actions.init.init_project(root=project_directory.strpath)
diff --git a/tests/actions/test_install.py b/tests/actions/test_install.py
new file mode 100644
index 0000000..45b44c0
--- /dev/null
+++ b/tests/actions/test_install.py
@@ -0,0 +1,96 @@
+# -*- coding=utf-8 -*-
+
+import passa.actions.install
+import passa.actions.add
+import passa.cli.options
+import passa.models.projects
+import pytest
+
+
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_install_one(project, is_dev):
+    add_kwargs = {
+        "project": project,
+        "packages": ["pytz",],
+        "editables": [],
+        "dev": is_dev,
+        "sync": False,
+        "clean": False
+    }
+    retcode = passa.actions.add.add_packages(**add_kwargs)
+    assert not retcode
+    lockfile_section = "default" if not is_dev else "develop"
+    assert 'pytz' in project.lockfile._data[lockfile_section].keys()
+    install = passa.actions.install.install(project=project, check=True, dev=is_dev, clean=False)
+    assert install == 0
+    assert project.env.is_installed("pytz") or project.is_installed("pytz")
+
+
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_install_one_with_deps(project, is_dev):
+    add_kwargs = {
+        "project": project,
+        "packages": ["requests",],
+        "editables": [],
+        "dev": is_dev,
+        "sync": False,
+        "clean": False
+    }
+    retcode = passa.actions.add.add_packages(**add_kwargs)
+    assert not retcode
+    lockfile_section = "default" if not is_dev else "develop"
+    assert 'requests' in project.lockfile._data[lockfile_section].keys()
+    assert 'idna' in project.lockfile._data[lockfile_section].keys()
+    install = passa.actions.install.install(project=project, check=True, dev=is_dev, clean=False)
+    assert install == 0
+    assert project.env.is_installed("requests") or project.is_installed("requests")
+    assert project.env.is_installed("idna") or project.is_installed("idna")
+
+
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_install_editable(project, is_dev):
+    add_kwargs = {
+        "project": project,
+        "packages": [],
+        "editables": ["git+https://github.com/sarugaku/shellingham.git@1.2.1#egg=shellingham",],
+        "dev": is_dev,
+        "sync": False,
+        "clean": False
+    }
+    retcode = passa.actions.add.add_packages(**add_kwargs)
+    assert not retcode
+    lockfile_section = "default" if not is_dev else "develop"
+    assert 'shellingham' in project.lockfile._data[lockfile_section].keys()
+    install = passa.actions.install.install(project=project, check=True, dev=is_dev, clean=False)
+    assert install == 0
+    project.reload()
+    assert (project.env.is_installed("shellingham") or
+                project.is_installed("shellingham")), list([dist.project_name for dist in project.env.get_distributions()])
+
+
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_install_sdist(project, is_dev):
+    add_kwargs = {
+        "project": project,
+        "packages": ["arrow",],
+        "editables": [],
+        "dev": is_dev,
+        "sync": False,
+        "clean": False
+    }
+    retcode = passa.actions.add.add_packages(**add_kwargs)
+    assert not retcode
+    lockfile_section = "default" if not is_dev else "develop"
+    assert 'arrow' in project.lockfile._data[lockfile_section].keys()
+    install = passa.actions.install.install(project=project, check=True, dev=is_dev, clean=False)
+    assert install == 0
+    project.reload()
+    assert project.env.is_installed("arrow") or project.is_installed("arrow")
diff --git a/tests/actions/test_lock.py b/tests/actions/test_lock.py
new file mode 100644
index 0000000..962493e
--- /dev/null
+++ b/tests/actions/test_lock.py
@@ -0,0 +1,53 @@
+# -*- coding=utf-8 -*-
+
+import passa.actions.lock
+import passa.actions.install
+import passa.cli.options
+import passa.models.projects
+import pytest
+
+
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_lock_one(project, is_dev):
+    line = "pytz"
+    project.add_line_to_pipfile(line, develop=is_dev)
+    retcode = passa.actions.lock.lock(project=project)
+    project.reload()
+    assert retcode == 0
+    lockfile_section = "default" if not is_dev else "develop"
+    assert 'pytz' in project.lockfile._data[lockfile_section].keys()
+    install = passa.actions.install.install(project=project, check=True, dev=is_dev, clean=False)
+    assert install == 0
+
+
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_lock_one_with_deps(project, is_dev):
+    line = "requests"
+    project.add_line_to_pipfile(line, develop=is_dev)
+    retcode = passa.actions.lock.lock(project=project)
+    project.reload()
+    assert retcode == 0
+    lockfile_section = "default" if not is_dev else "develop"
+    assert 'requests' in project.lockfile._data[lockfile_section].keys()
+    assert 'idna' in project.lockfile._data[lockfile_section].keys()
+    install = passa.actions.install.install(project=project, check=True, dev=is_dev, clean=False)
+    assert install == 0
+
+
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_lock_editable(project, is_dev):
+    line = "-e git+https://github.com/sarugaku/shellingham.git@1.2.1#egg=shellingham"
+    project.add_line_to_pipfile(line, develop=is_dev)
+    retcode = passa.actions.lock.lock(project=project)
+    project.reload()
+    assert retcode == 0
+    lockfile_section = "default" if not is_dev else "develop"
+    assert 'shellingham' in project.lockfile._data[lockfile_section].keys(), project.lockfile._data
+    install = passa.actions.install.install(project=project, check=True, dev=is_dev, clean=False)
+    assert install == 0
diff --git a/tests/actions/test_remove_and_sync.py b/tests/actions/test_remove_and_sync.py
new file mode 100644
index 0000000..f428a94
--- /dev/null
+++ b/tests/actions/test_remove_and_sync.py
@@ -0,0 +1,142 @@
+# -*- coding=utf-8 -*-
+
+import passa.actions.add
+import passa.actions.remove
+import passa.cli.options
+import passa.models.projects
+import pytest
+import vistir
+
+
+@pytest.mark.parametrize(
+    'sync', (True, False)
+)
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_remove_one(project, sync, is_dev):
+    pkg = "xlrd"
+    add_kwargs = {
+        "project": project,
+        "packages": [pkg,],
+        "editables": [],
+        "dev": is_dev,
+        "sync": sync,
+        "clean": False
+    }
+    retcode = passa.actions.add.add_packages(**add_kwargs)
+    assert not retcode
+    lockfile_section = "default" if not is_dev else "develop"
+    assert pkg in project.lockfile._data[lockfile_section].keys()
+    if sync:
+        assert project.env.is_installed(pkg) or project.is_installed(pkg)
+    remove = "default" if not is_dev else "dev"
+    retcode = passa.actions.remove.remove(project=project, packages=[pkg,], sync=sync, only=remove)
+    assert not retcode
+    project.reload()
+    assert pkg not in project.lockfile._data[lockfile_section].keys()
+    if sync:
+        assert not project.env.is_installed(pkg)
+
+
+@pytest.mark.parametrize(
+    'sync', (True, False),
+)
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_remove_one_with_deps(project, sync, is_dev):
+    add_kwargs = {
+        "project": project,
+        "packages": ["requests",],
+        "editables": [],
+        "dev": is_dev,
+        "sync": sync,
+        "clean": False
+    }
+    retcode = passa.actions.add.add_packages(**add_kwargs)
+    assert not retcode
+    lockfile_section = "default" if not is_dev else "develop"
+    assert 'requests' in project.lockfile._data[lockfile_section].keys()
+    assert 'idna' in project.lockfile._data[lockfile_section].keys()
+    if sync:
+        c = vistir.misc.run(["{0}".format(project.env.python), "-c", "import requests"],
+                                nospin=True, block=True, return_object=True)
+        assert c.returncode == 0, (c.out, c.err)
+        assert project.env.is_installed("requests") or project.is_installed("requests")
+        assert project.env.is_installed("idna") or project.is_installed("idna")
+    remove = "default" if not is_dev else "dev"
+    retcode = passa.actions.remove.remove(project=project, packages=["requests",], sync=sync, only=remove)
+    assert not retcode
+    project.reload()
+    assert "requests" not in project.lockfile._data[lockfile_section].keys()
+    assert "idna" not in project.lockfile._data[lockfile_section].keys()
+    if sync:
+        assert not project.env.is_installed("requests")
+        assert not project.env.is_installed("idna")
+
+
+@pytest.mark.parametrize(
+    'sync', (True, False),
+)
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_remove_editable(project, sync, is_dev):
+    add_kwargs = {
+        "project": project,
+        "packages": [],
+        "editables": ["git+https://github.com/sarugaku/shellingham.git@1.2.1#egg=shellingham",],
+        "dev": is_dev,
+        "sync": sync,
+        "clean": False
+    }
+    retcode = passa.actions.add.add_packages(**add_kwargs)
+    assert not retcode
+    lockfile_section = "default" if not is_dev else "develop"
+    assert 'shellingham' in project.lockfile._data[lockfile_section].keys()
+    if sync:
+        c = vistir.misc.run(["{0}".format(project.env.python), "-c", "import shellingham"],
+                                nospin=True, block=True, return_object=True)
+        assert c.returncode == 0, (c.out, c.err)
+        assert project.env.is_installed("shellingham") or project.is_installed("shellingham")
+    remove = "default" if not is_dev else "dev"
+    retcode = passa.actions.remove.remove(project=project, packages=["shellingham",], sync=sync, only=remove)
+    assert not retcode
+    project.reload()
+    assert "shellingham" not in project.lockfile._data[lockfile_section].keys()
+    if sync:
+        assert not project.env.is_installed("shellingham")
+
+
+@pytest.mark.parametrize(
+    'sync', (True, False),
+)
+@pytest.mark.parametrize(
+    'is_dev', (True, False)
+)
+def test_remove_sdist(project, is_dev, sync):
+    add_kwargs = {
+        "project": project,
+        "packages": ["arrow"],
+        "editables": [],
+        "dev": is_dev,
+        "sync": sync,
+        "clean": False
+    }
+    retcode = passa.actions.add.add_packages(**add_kwargs)
+    assert not retcode
+    lockfile_section = "default" if not is_dev else "develop"
+    assert 'arrow' in project.lockfile._data[lockfile_section].keys()
+    if sync:
+        c = vistir.misc.run(["{0}".format(project.env.python), "-c", "import arrow"],
+                                nospin=True, block=True, return_object=True)
+        assert c.returncode == 0, (c.out, c.err)
+        assert project.env.is_installed("arrow") or project.is_installed("arrow")
+    remove = "default" if not is_dev else "dev"
+    retcode = passa.actions.remove.remove(project=project, packages=["arrow",], sync=sync, only=remove)
+    assert not retcode
+    project.reload()
+    assert "arrow" not in project.lockfile._data[lockfile_section].keys()
+    if sync:
+        assert not project.env.is_installed("arrow")
diff --git a/tests/actions/test_upgrade.py b/tests/actions/test_upgrade.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/cli/__init__.py b/tests/cli/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/cli/test_add.py b/tests/cli/test_add.py
new file mode 100644
index 0000000..a6bcbda
--- /dev/null
+++ b/tests/cli/test_add.py
@@ -0,0 +1 @@
+# -*- coding=utf-8 -*-
diff --git a/tests/cli/test_clean.py b/tests/cli/test_clean.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/cli/test_freeze.py b/tests/cli/test_freeze.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/cli/test_init.py b/tests/cli/test_init.py
new file mode 100644
index 0000000..a6bcbda
--- /dev/null
+++ b/tests/cli/test_init.py
@@ -0,0 +1 @@
+# -*- coding=utf-8 -*-
diff --git a/tests/cli/test_install.py b/tests/cli/test_install.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/cli/test_lock.py b/tests/cli/test_lock.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/cli/test_remove.py b/tests/cli/test_remove.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/cli/test_sync.py b/tests/cli/test_sync.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/cli/test_upgrade.py b/tests/cli/test_upgrade.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..1ac4319
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,107 @@
+# -*- coding=utf-8 -*-
+import os
+import pytest
+import passa
+import passa.models.projects
+import passa.cli.options
+# import mork
+import passa.models.environments
+import pkg_resources
+import plette
+import sys
+import vistir
+
+from collections import deque
+
+
+DEFAULT_PIPFILE_CONTENTS = """
+[[source]]
+name = "pypi"
+url = "https://pypi.org/simple"
+verify_ssl = true
+
+[packages]
+
+[dev-packages]
+""".strip()
+
+
+@pytest.fixture(scope="session")
+def working_set_extension():
+    dists = set()
+    passa_dist = pkg_resources.get_distribution(pkg_resources.Requirement('passa'))
+    dists.add(passa_dist)
+    requirements = deque(passa_dist.requires(extras=('tests', 'virtualenv')))
+    while requirements:
+        req = requirements.popleft()
+        dist = pkg_resources.working_set.find(req)
+        dists.add(dist)
+        requirements.extend(dist.requires())
+    return dists
+
+
+@pytest.fixture(scope="function")
+def virtualenv(tmpdir_factory):
+    venv_dir = tmpdir_factory.mktemp("passa-testenv")
+    print("Creating virtualenv {0!r}".format(venv_dir.strpath))
+    c = vistir.misc.run([sys.executable, "-m", "virtualenv", venv_dir.strpath],
+                            return_object=True, block=True, nospin=True)
+    if c.returncode == 0:
+        print("Virtualenv created...")
+        return venv_dir
+    raise RuntimeError("Failed creating virtualenv for testing...{0!r}".format(c.err.strip()))
+
+
+class _Project(passa.cli.options.Project):
+    def __init__(self, root, environment=None, working_set_extension=[]):
+        self.path = root
+        self.working_set_extension = working_set_extension
+        self.env = environment
+        super(_Project, self).__init__(self.path, environment=environment)
+        self.pipfile_instance = vistir.compat.Path(self.pipfile_location)
+        self.lockfile_instance = vistir.compat.Path(self.lockfile_location)
+
+    def reload(self):
+        self._p = passa.models.projects.ProjectFile.read(
+            os.path.join(self.path, "Pipfile"),
+            plette.Pipfile,
+        )
+        self._l = passa.models.projects.ProjectFile.read(
+            os.path.join(self.path, "Pipfile.lock"),
+            plette.Lockfile,
+            invalid_ok=True,
+        )
+
+
+@pytest.fixture(scope="function")
+def project_directory(tmpdir_factory):
+    project_dir = tmpdir_factory.mktemp("passa-project")
+    project_dir.join("Pipfile").write(DEFAULT_PIPFILE_CONTENTS)
+    with vistir.contextmanagers.cd(project_dir.strpath):
+        yield project_dir
+
+
+@pytest.fixture
+def tmpvenv(virtualenv, tmpdir):
+    venv_srcdir = virtualenv.join("src").mkdir()
+    # venv = mork.virtualenv.VirtualEnv(virtualenv.strpath)
+    workingset = pkg_resources.WorkingSet(sys.path)
+    venv = passa.models.environments.Environment(prefix=virtualenv.strpath, is_venv=True,
+                                                    base_working_set=workingset)
+    venv.add_dist("passa")
+    venv.run(["pip", "install", "--upgrade", "mork", "setuptools"])
+    with vistir.contextmanagers.temp_environ():
+        os.environ["PACKAGEBUILDER_CACHE_DIR"] = tmpdir.strpath
+        os.environ["PIP_QUIET"] = "1"
+        os.environ["PIP_SRC"] = venv_srcdir.strpath
+        venv.is_installed = lambda x: any(d for d in venv.get_distributions() if d.project_name == x)
+        yield venv
+
+
+@pytest.fixture(scope="function")
+def project(project_directory, working_set_extension, tmpvenv):
+    # resolved = tmpvenv.resolve_dist(passa_dist, tmpvenv.base_working_set)
+    with tmpvenv.activated(extra_dists=list(working_set_extension)):
+        project = _Project(project_directory.strpath, environment=tmpvenv, working_set_extension=working_set_extension)
+        project.is_installed = lambda x: any(d for d in tmpvenv.get_working_set() if d.project_name == x)
+        yield project
diff --git a/tests/integration/__init__.py b/tests/integration/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tox.ini b/tox.ini
index 2bc8e1d..5c0a6dd 100644
--- a/tox.ini
+++ b/tox.ini
@@ -8,9 +8,13 @@ setenv =
     LC_ALL = en_US.UTF-8
 deps =
 	coverage
-	-e .[tests]
+    setuptools
+    pytest
+    pytest-timeout
+    pytest-sugar
+	-e .[tests,virtualenv]
 commands = coverage run --parallel -m pytest --timeout 300 []
-install_command = python -m pip install {opts} {packages}
+install_command = python -m pip install --upgrade {opts} {packages}
 usedevelop = True
 
 [testenv:coverage-report]
@@ -23,15 +27,15 @@ commands =
 [testenv:docs]
 deps =
     -r{toxinidir}/docs/requirements.txt
-    -e .[tests]
 commands =
     sphinx-build -d {envtmpdir}/doctrees -b html docs docs/build/html
     sphinx-build -d {envtmpdir}/doctrees -b man  docs docs/build/man
 
 [testenv:packaging]
 deps =
-    check-manifest
-    readme_renderer
+    setuptools
+    twine
+    readme_renderer[md]
 commands =
-    check-manifest
-    python setup.py check -m -r -s
+    python setup.py sdist bdist_wheel
+    twine check dist/*