Explicitly check case‐sensitivity of file system for tests (#19540)

Both macOS and Windows support using case‐sensitive file systems; this
fixes the test suite in those situations.

Author: emilazy

mypy/test/testcheck.py

@@ -5,6 +5,8 @@
 import os
 import re
 import sys
+import tempfile
+from pathlib import Path
 
 from mypy import build
 from mypy.build import Graph
@@ -46,15 +48,16 @@
 if sys.version_info < (3, 13):
     typecheck_files.remove("check-python313.test")
 
-# Special tests for platforms with case-insensitive filesystems.
-if sys.platform not in ("darwin", "win32"):
-    typecheck_files.remove("check-modules-case.test")
-
 
 class TypeCheckSuite(DataSuite):
     files = typecheck_files
 
     def run_case(self, testcase: DataDrivenTestCase) -> None:
+        if os.path.basename(testcase.file) == "check-modules-case.test":
+            with tempfile.NamedTemporaryFile(prefix="test", dir=".") as temp_file:
+                temp_path = Path(temp_file.name)
+                if not temp_path.with_name(temp_path.name.upper()).exists():
+                    pytest.skip("File system is not case‐insensitive")
         if lxml is None and os.path.basename(testcase.file) == "check-reports.test":
             pytest.skip("Cannot import lxml. Is it installed?")
         incremental = (

mypy/test/testfscache.py

@@ -4,7 +4,6 @@
 
 import os
 import shutil
-import sys
 import tempfile
 import unittest
 
@@ -83,7 +82,7 @@ def test_isfile_case_other_directory(self) -> None:
             assert self.isfile_case(os.path.join(other, "other_dir.py"))
             assert not self.isfile_case(os.path.join(other, "Other_Dir.py"))
             assert not self.isfile_case(os.path.join(other, "bar.py"))
-            if sys.platform in ("win32", "darwin"):
+            if os.path.exists(os.path.join(other, "PKG/other_dir.py")):
                 # We only check case for directories under our prefix, and since
                 # this path is not under the prefix, case difference is fine.
                 assert self.isfile_case(os.path.join(other, "PKG/other_dir.py"))