Use RealPathlibModule for all skipped modules

- avoids the use of FakePathLibPath in pathlib
- add _pytest.pathlib to skipped modules,
  fake isinstance check for RealPathlibPathModule
- prevents issue with _pytest.pathlib in pytest 7.0.0,
  which would cause all tests with fs fixture to fail
- see #666

5 files changed, 34 insertions, 19 deletions

diff --git a/CHANGES.md b/CHANGES.md
index e59b9c0..848d58a 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -10,6 +10,8 @@ The released versions correspond to PyPi releases.
   (see [#661](../../issues/661))
 * disallow `encoding` argument on binary `open()`
   (see [#664](../../issues/664))
+* fixed compatibility issue with pytest 7.0.0
+  (see [#666](../../issues/666))
 
 ## [Version 4.5.4](https://pypi.python.org/pypi/pyfakefs/4.5.4) (2022-01-12)
 Minor bugfix release.
diff --git a/pyfakefs/fake_filesystem_unittest.py b/pyfakefs/fake_filesystem_unittest.py
index c2ec11e..6633cb5 100644
--- a/pyfakefs/fake_filesystem_unittest.py
+++ b/pyfakefs/fake_filesystem_unittest.py
@@ -681,7 +681,6 @@ class Patcher:
         for name, module in list(sys.modules.items()):
             try:
                 if (self.use_cache and module in self.CACHED_MODULES or
-                        module in self.SKIPMODULES or
                         not inspect.ismodule(module)):
                     continue
             except Exception:
@@ -692,7 +691,8 @@ class Patcher:
                 if self.use_cache:
                     self.__class__.CACHED_MODULES.add(module)
                 continue
-            skipped = (any([sn.startswith(module.__name__)
+            skipped = (module in self.SKIPMODULES or
+                       any([sn.startswith(module.__name__)
                             for sn in self._skip_names]))
             module_items = module.__dict__.copy().items()
 
@@ -703,22 +703,22 @@ class Patcher:
                 for name, mod in modules.items():
                     self.__class__.SKIPPED_FS_MODULES.setdefault(
                         name, set()).add((module, mod.__name__))
-                continue
-
-            for name, mod in modules.items():
-                self.__class__.FS_MODULES.setdefault(name, set()).add(
-                    (module, mod.__name__))
-            functions = {name: fct for name, fct in
-                         module_items
-                         if self._is_fs_function(fct)}
-
-            for name, fct in functions.items():
-                self.__class__.FS_FUNCTIONS.setdefault(
-                    (name, fct.__name__, fct.__module__), set()).add(module)
-
-            # find default arguments that are file system functions
-            if self.patch_default_args:
-                self._find_def_values(module_items)
+            else:
+                for name, mod in modules.items():
+                    self.__class__.FS_MODULES.setdefault(name, set()).add(
+                        (module, mod.__name__))
+                functions = {name: fct for name, fct in
+                             module_items
+                             if self._is_fs_function(fct)}
+
+                for name, fct in functions.items():
+                    self.__class__.FS_FUNCTIONS.setdefault(
+                        (name, fct.__name__, fct.__module__),
+                        set()).add(module)
+
+                # find default arguments that are file system functions
+                if self.patch_default_args:
+                    self._find_def_values(module_items)
 
             if self.use_cache:
                 self.__class__.CACHED_MODULES.add(module)
diff --git a/pyfakefs/fake_pathlib.py b/pyfakefs/fake_pathlib.py
index 2b305e8..8868558 100644
--- a/pyfakefs/fake_pathlib.py
+++ b/pyfakefs/fake_pathlib.py
@@ -845,6 +845,12 @@ class RealPathlibPathModule:
     """Patches `pathlib.Path` by passing all calls to RealPathlibModule."""
     real_pathlib = None
 
+    @classmethod
+    def __instancecheck__(cls, instance):
+        # as we cannot derive from pathlib.Path, we fake
+        # the inheritance to pass isinstance checks - see #666
+        return isinstance(instance, PurePath)
+
     def __init__(self):
         if self.real_pathlib is None:
             self.__class__.real_pathlib = RealPathlibModule()
diff --git a/pyfakefs/pytest_plugin.py b/pyfakefs/pytest_plugin.py
index e8b95f3..43890f9 100644
--- a/pyfakefs/pytest_plugin.py
+++ b/pyfakefs/pytest_plugin.py
@@ -8,7 +8,7 @@ def my_fakefs_test(fs):
     fs.create_file('/var/data/xx1.txt')
     assert os.path.exists('/var/data/xx1.txt')
 """
-
+import _pytest
 import py
 import pytest
 
@@ -16,6 +16,7 @@ from pyfakefs.fake_filesystem_unittest import Patcher
 
 Patcher.SKIPMODULES.add(py)
 Patcher.SKIPMODULES.add(pytest)
+Patcher.SKIPMODULES.add(_pytest.pathlib)
 
 
 @pytest.fixture
diff --git a/pyfakefs/tests/fake_filesystem_test.py b/pyfakefs/tests/fake_filesystem_test.py
index b95db8f..f131d2f 100644
--- a/pyfakefs/tests/fake_filesystem_test.py
+++ b/pyfakefs/tests/fake_filesystem_test.py
@@ -1814,6 +1814,8 @@ class DiskSpaceTest(TestCase):
                 f.write('b' * 110)
                 with self.raises_os_error(errno.ENOSPC):
                     f.flush()
+        with self.open('bar.txt') as f:
+            self.assertEqual('', f.read())
 
     def test_disk_full_append(self):
         file_path = 'bar.txt'
@@ -1826,6 +1828,8 @@ class DiskSpaceTest(TestCase):
                 f.write('b' * 41)
                 with self.raises_os_error(errno.ENOSPC):
                     f.flush()
+        with self.open('bar.txt') as f:
+            self.assertEqual(f.read(), 'a' * 60)
 
     def test_disk_full_after_reopened_rplus_seek(self):
         with self.open('bar.txt', 'w') as f:
@@ -1838,6 +1842,8 @@ class DiskSpaceTest(TestCase):
                 f.write('b' * 60)
                 with self.raises_os_error(errno.ENOSPC):
                     f.flush()
+        with self.open('bar.txt') as f:
+            self.assertEqual(f.read(), 'a' * 60)
 
 
 class MountPointTest(TestCase):