Clear fs cache on session finish

- avoids problems with cached modules during session shutdown
- see pytest-dev#866

Author: mrbean-bremen

.github/workflows/testsuite.yml

@@ -112,6 +112,7 @@ jobs:
         run: |
           pip install -r requirements.txt
           pip install -U pytest==${{ matrix.pytest-version }}
+          pip install opentimelineio
           if [[ '${{ matrix.pytest-version }}' == '4.0.2' ]]; then
              pip install -U attrs==19.1.0
           fi

CHANGES.md

@@ -3,6 +3,9 @@ The released versions correspond to PyPI releases.
 
 ## Unreleased
 
+### Fixes
+* Clear the patched module cache on session shutdown (pytest only)
+  (see [#866](../../issues/866)).
 
 ## [Version 5.2.3](https://pypi.python.org/pypi/pyfakefs/5.2.3) (2023-07-10)
 Adds compatibility with PyPy 3.10 and Python 3.12.

docs/usage.rst

@@ -625,8 +625,7 @@ use_cache
 .........
 If True (the default), patched and non-patched modules are cached between tests
 to avoid the performance hit of the file system function lookup (the
-patching itself is reverted after each test). As this is a new
-feature, this argument allows to turn it off in case it causes any problems:
+patching itself is reverted after each test). This argument allows to turn it off in case it causes any problems:
 
 .. code:: python
 
@@ -635,9 +634,22 @@ feature, this argument allows to turn it off in case it causes any problems:
       fake_fs.create_file("foo", contents="test")
       ...
 
-Please write an issue if you encounter any problem that can be fixed by using
-this parameter. Note that this argument may be removed in a later version, if
-no problems come up.
+If using ``pytest``, the cache is always cleared before the final test shutdown, as there has been a problem
+happening on shutdown related to removing the cached modules.
+This does not happen for other test methods so far.
+
+If you think you have encountered a similar problem with ``unittest``, you may try to clear the cache
+during module shutdown using the class method for clearing the cache:
+
+.. code:: python
+
+  from pyfakefs.fake_filesystem_unittest import Patcher
+
+
+  def tearDownModule():
+      Patcher.clear_fs_cache()
+
+Please write an issue if you encounter any problem that can be fixed by using this parameter.
 
 If you want to clear the cache just for a specific test instead, you can call
 ``clear_cache`` on the ``Patcher`` or the ``fake_filesystem`` instance:

pyfakefs/fake_filesystem_unittest.py

@@ -629,13 +629,19 @@ def __init__(
         self._dyn_patcher: Optional[DynamicPatcher] = None
         self._patching = False
 
-    def clear_cache(self) -> None:
+    @classmethod
+    def clear_fs_cache(cls) -> None:
         """Clear the module cache."""
-        self.__class__.CACHED_MODULES = set()
-        self.__class__.FS_MODULES = {}
-        self.__class__.FS_FUNCTIONS = {}
-        self.__class__.FS_DEFARGS = []
-        self.__class__.SKIPPED_FS_MODULES = {}
+        print("Clearing the cache")
+        cls.CACHED_MODULES = set()
+        cls.FS_MODULES = {}
+        cls.FS_FUNCTIONS = {}
+        cls.FS_DEFARGS = []
+        cls.SKIPPED_FS_MODULES = {}
+
+    def clear_cache(self) -> None:
+        """Clear the module cache (convenience instance method)."""
+        self.__class__.clear_fs_cache()
 
     def _init_fake_module_classes(self) -> None:
         # IMPORTANT TESTING NOTE: Whenever you add a new module below, test

pyfakefs/pytest_plugin.py

@@ -8,6 +8,7 @@ def my_fakefs_test(fs):
     fs.create_file('/var/data/xx1.txt')
     assert os.path.exists('/var/data/xx1.txt')
 """
+
 import py
 import pytest
 from _pytest import capture
@@ -17,7 +18,7 @@ def my_fakefs_test(fs):
 try:
     from _pytest import pathlib
 except ImportError:
-    pathlib = None
+    pathlib = None  # type:ignore[assignment]
 
 Patcher.SKIPMODULES.add(py)
 Patcher.SKIPMODULES.add(pytest)
@@ -73,3 +74,9 @@ def fs_session(request):
     patcher.setUp()
     yield patcher.fs
     patcher.tearDown()
+
+
+@pytest.hookimpl(tryfirst=True)
+def pytest_sessionfinish(session, exitstatus):
+    """Make sure that the cache is cleared before the final test shutdown."""
+    Patcher.clear_fs_cache()