fix(testing): correct delete_dir prefix matching in stateful tests

changes/3977.bugfix.md

@@ -0,0 +1 @@
+Fix flaky stateful test bookkeeping when `delete_dir` matches string prefixes instead of true directory descendants. Previously a path such as `6/faNT…` could be incorrectly removed when deleting `6/f`. (See [issue #3977](https://github.com/zarr-developers/zarr-python/issues/3977).)

src/zarr/testing/stateful.py

@@ -306,7 +306,7 @@ def delete_dir(self, data: DataObject) -> None:
 
         matches = set()
         for node in self.all_groups | self.all_arrays:
-            if node.startswith(path):
+            if node == path or node.startswith(path + "/"):
                 matches.add(node)
         self.all_groups = self.all_groups - matches
         self.all_arrays = self.all_arrays - matches

tests/test_store/test_stateful.py

@@ -49,3 +49,5 @@ def mk_test_instance_sync() -> ZarrStoreStateMachine:
         # But LocalStore, directories can hang around even after a key is delete-d.
         pytest.skip(reason="Test isn't suitable for LocalStore.")
     run_state_machine_as_test(mk_test_instance_sync)  # type: ignore[no-untyped-call]
+
+