Fix test isolation for clear_import_cache utility (#36345)

* test fixup

* test fixup

* fixing tests for unused imports

* style fixes

* fix

* style fixes

* styke fix

* remove isolated module cache

* rm custom subprocess defination

* run using exsiting fn

* style fixup

* make fixup

* remove redundant comments

* rm redundat skipif + style changes

tests/utils/test_import_utils.py

@@ -1,23 +1,26 @@
 import sys
 
+from transformers.testing_utils import run_test_using_subprocess
 from transformers.utils.import_utils import clear_import_cache
 
 
+@run_test_using_subprocess
 def test_clear_import_cache():
-    # Import some transformers modules
+    """Test the clear_import_cache function."""
 
-    # Get initial module count
+    # Save initial state
     initial_modules = {name: mod for name, mod in sys.modules.items() if name.startswith("transformers.")}
+    assert len(initial_modules) > 0, "No transformers modules loaded before test"
 
-    # Verify we have some modules loaded
-    assert len(initial_modules) > 0
-
-    # Clear cache
+    # Execute clear_import_cache() function
     clear_import_cache()
 
-    # Check modules were removed
+    # Verify modules were removed
     remaining_modules = {name: mod for name, mod in sys.modules.items() if name.startswith("transformers.")}
-    assert len(remaining_modules) < len(initial_modules)
+    assert len(remaining_modules) < len(initial_modules), "No modules were removed"
 
-    # Verify we can reimport
-    assert "transformers" in sys.modules
+    # Import and verify module exists
+    from transformers.models.auto import modeling_auto
+
+    assert "transformers.models.auto.modeling_auto" in sys.modules
+    assert modeling_auto.__name__ == "transformers.models.auto.modeling_auto"