Move get_test_dirs to a separate file

tests/hierarchy/get_test_dirs.py

@@ -0,0 +1,21 @@
+# Copyright (c) Jupyter Development Team.
+# Distributed under the terms of the Modified BSD License.
+from pathlib import Path
+
+from tests.hierarchy.images_hierarchy import IMAGE_PARENT
+
+THIS_DIR = Path(__file__).parent.resolve()
+IMAGE_SPECIFIC_TESTS_DIR = THIS_DIR.parent / "image_specific_tests"
+
+assert IMAGE_SPECIFIC_TESTS_DIR.exists(), f"{IMAGE_SPECIFIC_TESTS_DIR} does not exist."
+
+
+def get_test_dirs(image: str | None) -> list[Path]:
+    if image is None:
+        return []
+
+    test_dirs = get_test_dirs(IMAGE_PARENT[image])
+    current_test_dir = IMAGE_SPECIFIC_TESTS_DIR / image
+    assert current_test_dir.exists(), f"{current_test_dir} does not exist."
+    test_dirs.append(current_test_dir)
+    return test_dirs