Conftest file is loaded multiple times

[wassupxP]

Dear Pytest team,
I’ve encountered a bug on Windows where conftest.py is loaded multiple times if the path to the test files is specified with differing case on a case-insensitive file system. This behavior triggers the following error (on minimal reproduction example) - ValueError: option names {'--dummy-option'} already added

Minimal reproduction example:

pytest_bug.zip

Steps to reproduce:

1. unzip pytest_bug.zip
2. python -m pytest .\pytest_bug\Reproducer\
   (note that running python -m pytest .\pytest_bug\reproducer\ will finish with 0 collected tests as expected)

Pip list output and OS version

OS version: Windows 11
Python Version: 3.12.9

(.venv) PS C:\venvs\reproducer\pytest_bug> python -m pip list  
Package   Version
--------- -------
colorama  0.4.6
iniconfig 2.0.0
packaging 24.2
pip       24.3.1
pluggy    1.5.0
pytest    8.3.5

Potentional fix

Resolving the path fixes the issue, but I am not sure whether it might not have impact on something else.

$ git diff
diff --git a/src/_pytest/config/__init__.py b/src/_pytest/config/__init__.py
index 56b047196..39f61daaf 100644
--- a/src/_pytest/config/__init__.py
+++ b/src/_pytest/config/__init__.py
@@ -643,7 +643,7 @@ class PytestPluginManager(PluginManager):
         if self._noconftest:
             return

-        directory = self._get_directory(path)
+        directory = self._get_directory(path.resolve())

Thank you.

[ugomancz]

I think the problem might actually be in the PytestPluginManager._set_initial_conftests method.

In that method, conftest plugins are loaded from the directories provided as CLI arguments and the paths aren't being normalized, which results in loading the conftest from a path with Reproducer (wrong capital letter), which works because Windows is case-insensitive.

        for initial_path in args:
            path = str(initial_path)
            # remove node-id syntax
            i = path.find("::")
            if i != -1:
                path = path[:i]
            anchor = absolutepath(invocation_dir / path)

            # Ensure we do not break if what appears to be an anchor
            # is in fact a very long option (#10169, #11394).
            if safe_exists(anchor):
                self._try_load_conftest(
                    anchor,
                    importmode,
                    rootpath,
                    consider_namespace_packages=consider_namespace_packages,
                )
                foundanchor = True

However this causes the conftest to be saved with a plugin name that doesn't correspond to its actual path later in PytestPluginManager._importconftest, which just turns the Path object to a string, preserving the wrong capital letter.

        conftestpath_plugin_name = str(conftestpath)
        existing = self.get_plugin(conftestpath_plugin_name)
        if existing is not None:
            return cast(types.ModuleType, existing)

So later, during test collection when the paths are normalized correctly, when this conftest is encountered again, self.get_plugin returns None as the conftest was previously saved with Reproducer in the conftest_plugin_name, but now it has reproducer in it.

I think the correct fix for this would be to normalize the paths to locations from CLI arguments before loading the initial conftests, by changing this line in PytestPluginManager._set_initial_conftests

diff --git a/config/__init__.py b/config/__init__.py
index 4588f4d..6ec60d0 100644
--- a/config/__init__.py
+++ b/config/__init__.py
@@ -573,7 +573,7 @@ class PytestPluginManager(PluginManager):
             i = path.find("::")
             if i != -1:
                 path = path[:i]
-            anchor = absolutepath(invocation_dir / path)
+            anchor = absolutepath(invocation_dir / path).resolve()

             # Ensure we do not break if what appears to be an anchor
             # is in fact a very long option (#10169, #11394).

I would really appreciate it if someone more experienced could give their opinion. If this fix is correct, I can put together a pull request.