Add test for cached_fsdecode function

Co-authored-by: eleanorjboyd <26030610+eleanorjboyd@users.noreply.github.com>

Author: Copilot

python_files/tests/pytestadapter/test_utils.py

@@ -12,7 +12,7 @@
 
 script_dir = pathlib.Path(__file__).parent.parent.parent
 sys.path.append(os.fspath(script_dir))
-from vscode_pytest import has_symlink_parent  # noqa: E402
+from vscode_pytest import cached_fsdecode, has_symlink_parent  # noqa: E402
 
 
 def test_has_symlink_parent_with_symlink():
@@ -33,3 +33,25 @@ def test_has_symlink_parent_without_symlink():
     folder_path = TEST_DATA_PATH / "unittest_folder" / "test_add.py"
     # Check that has_symlink_parent correctly identifies that there are no symbolic links
     assert not has_symlink_parent(folder_path)
+
+
+def test_cached_fsdecode():
+    """Test that cached_fsdecode correctly caches path-to-string conversions."""
+    # Create a test path
+    test_path = TEST_DATA_PATH / "simple_pytest.py"
+
+    # First call should compute and cache
+    result1 = cached_fsdecode(test_path)
+    assert result1 == os.fspath(test_path)
+    assert isinstance(result1, str)
+
+    # Second call should return cached value (same object)
+    result2 = cached_fsdecode(test_path)
+    assert result2 == result1
+    assert result2 is result1  # Should be the same object from cache
+
+    # Different path should be cached independently
+    test_path2 = TEST_DATA_PATH / "parametrize_tests.py"
+    result3 = cached_fsdecode(test_path2)
+    assert result3 == os.fspath(test_path2)
+    assert result3 != result1