gh-109295: Skip test_generated_cases if different mount drives

On Windows, skip the test if the current working directory and the
Python source code directory have different mount drives. It happens
if the temporary directory is on a different mount drive than the
Python source code.

Author: vstinner

Lib/test/test_generated_cases.py

@@ -1,11 +1,31 @@
 import contextlib
+import os
+import sys
 import tempfile
 import unittest
-import os
 
 from test import support
 from test import test_tools
 
+
+def skip_if_different_mount_drives():
+    if sys.platform != 'win32':
+        return
+    ROOT = os.path.dirname(os.path.dirname(__file__))
+    root_drive = os.path.splitroot(ROOT)[0]
+    cwd_drive = os.path.splitroot(os.getcwd())[0]
+    if root_drive != cwd_drive:
+        # generate_cases.py uses relpath() which raises ValueError if ROOT
+        # and the current working different have different mount drives
+        # (on Windows).
+        raise unittest.SkipTest(
+            f"the current working directory and the Python source code "
+            f"directory have different mount drives "
+            f"({cwd_drive} and {root_drive})"
+        )
+skip_if_different_mount_drives()
+
+
 test_tools.skip_if_missing('cases_generator')
 with test_tools.imports_under_tool('cases_generator'):
     import generate_cases