Unload all modules loaded during the test

- these module can still hold references to fake modules
- modules already loaded at test start are not affected
- see pytest-dev#501 and pytest-dev#427

CHANGES.md

@@ -14,9 +14,9 @@ the proposed changes so you can be ready.
 
 ### Fixes
   * fixed side effect of calling `DirEntry.stat()` under Windows (changed 
-    st_nlink) ([#502](../../issues/502))
-  * fixed a problem related to patching `distutils` functions
-    ([#501](../../issues/501))
+    st_nlink) (see [#502](../../issues/502))
+  * fixed problem of fake modules still referenced after a test in modules 
+    loaded during the test (see [#501](../../issues/501) and [#427](../../issues/427))
   * correctly handle missing read permission for parent directory
     (see [#496](../../issues/496))
   * raise for `os.scandir` with non-existing directory

pyfakefs/fake_filesystem_unittest.py

@@ -42,15 +42,11 @@
 import tempfile
 import unittest
 import warnings
-import zipfile  # noqa: F401 make sure it gets correctly stubbed, see #427
-import distutils.file_util  # noqa: F401 same reason - see #501
 
+from pyfakefs.deprecator import Deprecator
 from pyfakefs.fake_filesystem import set_uid, set_gid, reset_ids
-
 from pyfakefs.helpers import IS_PY2, IS_PYPY
 
-from pyfakefs.deprecator import Deprecator
-
 try:
     from importlib.machinery import ModuleSpec
 except ImportError:
@@ -643,14 +639,15 @@ def __exit__(self, *args):
 
 class DynamicPatcher(object):
     """A file loader that replaces file system related modules by their
-    fake implementation if they are loaded after calling `setupPyFakefs()`.
+    fake implementation if they are loaded after calling `setUpPyfakefs()`.
     Implements the protocol needed for import hooks.
     """
 
     def __init__(self, patcher):
         self._patcher = patcher
         self.sysmodules = {}
         self.modules = self._patcher.fake_modules
+        self._loaded_module_names = set()
 
         # remove all modules that have to be patched from `sys.modules`,
         # otherwise the find_... methods will not be called
@@ -668,10 +665,18 @@ def cleanup(self):
         for module in self._patcher.modules_to_reload:
             if module.__name__ in sys.modules:
                 reload(module)
+        reloaded_module_names = [module.__name__
+                                 for module in self._patcher.modules_to_reload]
+        # force all modules loaded during the test to reload on next use,
+        # to ensure that no faked modules are still hold in these modules
+        for name in self._loaded_module_names:
+            if name in sys.modules and name not in reloaded_module_names:
+                del sys.modules[name]
 
     def needs_patch(self, name):
         """Check if the module with the given name shall be replaced."""
         if name not in self.modules:
+            self._loaded_module_names.add(name)
             return False
         if (name in sys.modules and
                 type(sys.modules[name]) == self.modules[name]):

pyfakefs/tests/dynamic_patch_test.py

@@ -11,7 +11,7 @@
 # limitations under the License.
 
 """
-Tests for patching modules loaded after `setupPyfakefs()`.
+Tests for patching modules loaded after `setUpPyfakefs()`.
 """
 import sys
 import unittest