diff --git a/tests/unit/test_documentation_consistency.py b/tests/unit/test_documentation_consistency.py
index 63ea43e..5dc2189 100644
--- a/tests/unit/test_documentation_consistency.py
+++ b/tests/unit/test_documentation_consistency.py
@@ -704,6 +704,18 @@ class DocumentationConsistencyTests(unittest.TestCase):
         self.assertIsInstance(missing_by_doc["complete-release-index.md"], tuple)
         self.assertEqual(docs_by_name, original_docs_by_name)
 
+    def test_training_m49_release_index_per_doc_helper_handles_empty_docs_without_mutation(self) -> None:
+        complete_release_doc = "\n".join(TRAINING_M41_RELEASE_INDEX_DOC_SNIPPETS)
+        docs_by_name = {"complete-release-index.md": complete_release_doc}
+        original_docs_by_name = dict(docs_by_name)
+
+        empty_missing_by_doc = _release_index_missing_required_snippets_by_doc({})
+        complete_missing_by_doc = _release_index_missing_required_snippets_by_doc(docs_by_name)
+
+        self.assertEqual(empty_missing_by_doc, {})
+        self.assertEqual(docs_by_name, original_docs_by_name)
+        self.assertEqual(complete_missing_by_doc["complete-release-index.md"], ())
+
     def test_training_m41_release_index_inventory_shape_is_stable(self) -> None:
         module_tree = ast.parse(Path(__file__).read_text(encoding="utf-8"))
         inventory_assignments = [