Normalize conftest paths

Refs #9765. While this is probably not needed for fixing the `assert mod
not in mods` bug (previous commit takes care of it), I believe this is
the right thing to do to avoid other inconsistencies (see discussion in
issue).

Author: bluetech

src/_pytest/config/__init__.py

@@ -340,12 +340,20 @@ def _prepareconfig(
         raise
 
 
-def _get_directory(path: Path) -> Path:
-    """Get the directory of a path - itself if already a directory."""
+def _get_conftest_directory(path: Path) -> Path:
+    """Get the conftest directory of a path.
+
+    If the path is a directory, this is the path itself, otherwise its parent
+    directory.
+
+    The path is normalized to remove differences between different sources of
+    conftest paths which can cause inconsistencies (issue #9765).
+    """
     if path.is_file():
-        return path.parent
+        conftest_directory = path.parent
     else:
-        return path
+        conftest_directory = path
+    return Path(os.path.normcase(os.path.normpath(conftest_directory)))
 
 
 def _get_legacy_hook_marks(
@@ -407,10 +415,10 @@ def __init__(self) -> None:
         # If set, conftest loading is skipped.
         self._noconftest = False
 
-        # _getconftestmodules()'s call to _get_directory() causes a stat
+        # _getconftestmodules()'s call to _get_conftest_directory() causes a stat
         # storm when it's called potentially thousands of times in a test
         # session (#9478), often with the same path, so cache it.
-        self._get_directory = lru_cache(256)(_get_directory)
+        self._get_conftest_directory = lru_cache(256)(_get_conftest_directory)
 
         # plugins that were explicitly skipped with pytest.skip
         # list of (module name, skip reason)
@@ -595,7 +603,7 @@ def _loadconftestmodules(
         if self._noconftest:
             return
 
-        directory = self._get_directory(path)
+        directory = self._get_conftest_directory(path)
 
         # Optimization: avoid repeated searches in the same directory.
         # Assumes always called with same importmode and rootpath.
@@ -615,7 +623,7 @@ def _loadconftestmodules(
         self._dirpath2confmods[directory] = clist
 
     def _getconftestmodules(self, path: Path) -> Sequence[types.ModuleType]:
-        directory = self._get_directory(path)
+        directory = self._get_conftest_directory(path)
         return self._dirpath2confmods.get(directory, ())
 
     def _rget_with_confmod(

testing/test_pluginmanager.py

@@ -110,25 +110,30 @@ def test_conftestpath_case_sensitivity(self, pytester: Pytester) -> None:
         conftest = pytester.path.joinpath("tests/conftest.py")
         conftest_upper_case = pytester.path.joinpath("TESTS/conftest.py")
 
-        mod = config.pluginmanager._importconftest(
+        config.pluginmanager._loadconftestmodules(
             conftest,
             importmode="prepend",
             rootpath=pytester.path,
         )
-        plugin = config.pluginmanager.get_plugin(str(conftest))
-        assert plugin is mod
+        plugins = config.pluginmanager._getconftestmodules(
+            conftest,
+        )
+        assert len(plugins) == 1
 
-        mod_uppercase = config.pluginmanager._importconftest(
+        config.pluginmanager._loadconftestmodules(
             conftest_upper_case,
             importmode="prepend",
             rootpath=pytester.path,
         )
-        plugin_uppercase = config.pluginmanager.get_plugin(str(conftest_upper_case))
-        assert plugin_uppercase is mod_uppercase
+        # conftest paths are normalized, so the plugin is registered in
+        # lower-case and the mod is not re-imported.
+        plugins_upper_case = config.pluginmanager._getconftestmodules(
+            conftest_upper_case,
+        )
+        assert plugins_upper_case == plugins
 
-        # No str(conftestpath) normalization so conftest should be imported
-        # twice and modules should be different objects
-        assert mod is not mod_uppercase
+        plugin_uppercase = config.pluginmanager.get_plugin(str(conftest_upper_case))
+        assert plugin_uppercase is None
 
     def test_hook_tracing(self, _config_for_test: Config) -> None:
         pytestpm = _config_for_test.pluginmanager  # fully initialized with plugins