Test install from PyPI with fast-deps

tests/functional/test_fast_deps.py

@@ -0,0 +1,27 @@
+import json
+
+from pip._vendor.packaging.utils import canonicalize_name
+from pytest import mark
+
+
+def assert_installed(script, names):
+    list_output = json.loads(script.pip('list', '--format=json').stdout)
+    installed = {canonicalize_name(item['name']) for item in list_output}
+    assert installed.issuperset(map(canonicalize_name, names))
+
+
+@mark.network
+@mark.parametrize(('spec', 'expected'), (
+    ('mypy==0.782', (
+        'mypy', 'mypy-extensions', 'typed-ast', 'typing-extensions',
+    )),
+    ('mypy[dmypy]==0.782', (
+        'mypy', 'mypy-extensions', 'typed-ast', 'typing-extensions', 'psutil',
+    )),
+))
+def test_install_from_pypi(spec, expected, script):
+    script.pip(
+        'install', '--use-feature=2020-resolver', '--use-feature=fast-deps',
+        spec, allow_stderr_warning=True,
+    )
+    assert_installed(script, expected)