test(utils): add test for virtualenv

This test is written as to allow for an easy extension, so that testing for
unconventional environments can be integrated rapidly. It mocks all parts
necessary to ensure that all combinations can be tested, without being too
verbose.

Author: ByteB4rb1e

tests/unit/test_utils.py

@@ -1,10 +1,15 @@
 import os
+import sys
+import sysconfig
+from contextlib import ExitStack
+import importlib
 from unittest import mock
+from unittest.mock import MagicMock, patch
 
 import pytest
 
 from pipenv.exceptions import PipenvUsageError
-from pipenv.utils import dependencies, indexes, internet, shell, toml
+from pipenv.utils import dependencies, indexes, internet, shell, toml, virtualenv
 
 # Pipfile format <-> requirements.txt format.
 DEP_PIP_PAIRS = [
@@ -547,3 +552,80 @@ def test_is_env_truthy_does_not_exisxt(self, monkeypatch):
         name = "ZZZ"
         monkeypatch.delenv(name, raising=False)
         assert shell.is_env_truthy(name) is False
+
+    @pytest.mark.utils
+    @pytest.mark.parametrize(
+        "os_name, platform, version, preferred_schemes, expected",
+        [
+            ("nt", "win32", "any",{'prefix': 'posix_prefix'}, 'foobar/bin'),
+            ("nt", "win32", "GCC",{'prefix': 'posix_prefix'}, 'foobar/bin'),
+            ("nt", "win32", "GCC", {'prefix': 'nt'}, 'foobar/bin'),
+            ("nt", "win32", "any", {'prefix': 'nt'}, 'foobar/Scripts'),
+            ("nt", "win32", "any", {'prefix': 'venv'}, 'foobar/Scripts'),
+            ("nt", "win32", "GCC", {'prefix': 'venv'}, 'foobar/bin'),
+        ]
+    )
+    def test_virtualenv_scripts_dir(self, os_name, platform, version, preferred_schemes, expected):
+        """Test for CPython compiled against various platforms
+
+        To simulate the differing environments as best as possible, we're
+        mocking `os.name`, and `sys.platform`, and
+        `sysconfig._get_preferred_schemes` as this is the lowest we must go to
+        have full control for mocking all possible combinations relevant for the
+        function we're testing here. MSYS2 is the most extreme edge-case I could
+        find, since it patches sysconfig at compile time.
+
+        References (CPython main branch is also applicable to 3.12 branch):
+
+            - https://github.com/msys2/MINGW-packages/blob/master/mingw-w64-python/0017-sysconfig-treat-MINGW-builds-as-POSIX-builds.patch
+            - https://github.com/python/cpython/blob/main/Lib/sysconfig/__init__.py#L28
+            - https://github.com/python/cpython/blob/main/Include/cpython/initconfig.h#L209
+            - https://github.com/python/cpython/blob/main/Python/sysmodule.c#L3894
+            - https://github.com/python/cpython/blob/main/Modules/getpath.py#L227
+
+        :param os_name: os.name
+        :param platform: sys.platform
+        :param version: sys.version
+        :param preferred_schemes: sysconfig._get_preferred_schemes()
+        """
+        with ExitStack() as stack:
+            stack.enter_context(patch.object(os, 'name', os_name))
+            stack.enter_context(patch.object(sys, 'platform', platform))
+            stack.enter_context(patch.object(sys, 'version', version))
+
+            # ensure, that when the test suite is executed from within a venv,
+            # that this does not trigger defaulting to choosing the venv prefix
+            if preferred_schemes['prefix'] != 'venv':
+                stack.enter_context(patch.object(sys, 'prefix', sys.base_prefix))
+
+            # we need to unload sysconfig, as well as the virtualenv util
+            # module, as a constant dependent on os.name
+            # and sys.version is being initialized during import, which we need
+            # to rewrite to be able to simulate different platforms and patches
+            # applied by CPython distributors.
+            if "sysconfig" in importlib.sys.modules:
+                del importlib.sys.modules["sysconfig"]
+            if "pipenv.utils.virtualenv" in importlib.sys.modules:
+                del importlib.sys.modules["pipenv.utils.virtualenv"]
+
+            sysconfig = importlib.import_module("sysconfig")
+            virtualenv = importlib.import_module("pipenv.utils.virtualenv")
+
+            # MSYS2 specific reversion of PATCH #23, which seems to be
+            # unnecessary, as the logic for correct platform switching is
+            # already handled by PATCH #17 (see references of this test) and
+            # also introduces inconsistencies. This overwrite only applies to a
+            # single parameter set though. As soon as the issue is resolved,
+            # this MSYS2 specific override can be removed 
+            #
+            # The issue is tracked here: https://github.com/msys2/MINGW-packages/issues/23992
+            # MSYS2-specific PATCH #23: https://github.com/msys2/MINGW-packages/blob/c8e881f77f804dd1721f7ff90e2931593eb6ac1a/mingw-w64-python/0023-sysconfig-mingw-sysconfig-like-posix.patch#L24
+            if preferred_schemes['prefix'] == 'nt' and 'GCC' not in version:
+                sysconfig._INSTALL_SCHEMES['nt']['scripts'] = '{base}/Scripts'
+
+            stack.enter_context(patch.object(
+                sysconfig, "_get_preferred_schemes", return_value=preferred_schemes
+            ))
+
+            assert str(virtualenv.virtualenv_scripts_dir('foobar')) == expected
+