Add PEP 668 functional tests

Author: uranusjr

tests/functional/test_pep668.py

@@ -0,0 +1,66 @@
+import textwrap
+from typing import List
+
+import pytest
+
+from tests.lib import PipTestEnvironment, create_basic_wheel_for_package
+from tests.lib.venv import VirtualEnvironment
+
+
+@pytest.fixture()
+def patch_check_externally_managed(virtualenv: VirtualEnvironment) -> None:
+    # Since the tests are run from a virtual environment, and we can't
+    # guarantee access to the actual stdlib location (where EXTERNALLY-MANAGED
+    # needs to go into), we patch the check to always raise a simple message.
+    virtualenv.sitecustomize = textwrap.dedent(
+        """\
+        from pip._internal.exceptions import ExternallyManagedEnvironment
+        from pip._internal.utils import misc
+
+        def check_externally_managed():
+            raise ExternallyManagedEnvironment("I am externally managed")
+
+        misc.check_externally_managed = check_externally_managed
+        """
+    )
+
+
+@pytest.mark.parametrize(
+    "arguments",
+    [
+        pytest.param(["install"], id="install"),
+        pytest.param(["install", "--user"], id="install-user"),
+        pytest.param(["uninstall", "-y"], id="uninstall"),
+    ],
+)
+@pytest.mark.usefixtures("patch_check_externally_managed")
+def test_fails(script: PipTestEnvironment, arguments: List[str]) -> None:
+    result = script.pip(*arguments, "pip", expect_error=True)
+    assert "I am externally managed" in result.stderr
+
+
+@pytest.mark.parametrize(
+    "arguments",
+    [
+        pytest.param(["install", "--root"], id="install-root"),
+        pytest.param(["install", "--prefix"], id="install-prefix"),
+        pytest.param(["install", "--target"], id="install-target"),
+    ],
+)
+@pytest.mark.usefixtures("patch_check_externally_managed")
+def test_allows_if_out_of_environment(
+    script: PipTestEnvironment,
+    arguments: List[str],
+) -> None:
+    wheel = create_basic_wheel_for_package(script, "foo", "1.0")
+    result = script.pip(*arguments, script.scratch_path, wheel.as_uri())
+    assert "Successfully installed foo-1.0" in result.stdout
+    assert "I am externally managed" not in result.stderr
+
+
+@pytest.mark.usefixtures("patch_check_externally_managed")
+def test_allows_install_dry_run(script: PipTestEnvironment) -> None:
+    wheel = create_basic_wheel_for_package(script, "foo", "1.0")
+    result = script.pip("install", "--dry-run", wheel.as_uri())
+    assert "Would install foo-1.0" in result.stdout
+    assert "I am externally managed" not in result.stderr