tests: update missed coverage in db layer

tests/unit/layer/db_layer/datastore/test_backend.py

@@ -29,6 +29,9 @@ def test_read_write_simple(datastore_emulator) -> None:
 
     entity = layer.backend.client.get(child_key)  # type: ignore
     assert entity["value"] == "val"
+    assert layer.get("key") == "val"
+    assert layer.get("non_existent_key") is None
+    assert layer.get("non_existent_key", "default_val") == "default_val"
 
 
 def test_read_write(datastore_emulator) -> None:
@@ -46,6 +49,7 @@ def test_read_write(datastore_emulator) -> None:
 
     data = layer[idx_user]
     assert data == data_user
+    assert layer[("key0", "col1")] == "val1"
 
 
 def test_with_changes(datastore_emulator) -> None:

zetta_utils/layer/db_layer/datastore/backend.py

@@ -83,7 +83,7 @@ def __contains__(self, idx: str) -> bool:
         parent_key = self.client.key("Row", idx)
         return self.client.get(parent_key) is not None
 
-    def __len__(self) -> int:
+    def __len__(self) -> int:  # pragma: no cover # no emulator support
         count_query = self.client.aggregation_query(self.client.query(kind="Row")).count()
         for aggregation_results in count_query.fetch():
             for aggregation in aggregation_results:

zetta_utils/layer/db_layer/layer.py

@@ -196,7 +196,7 @@ def __setitem__(self, idx, data):
     def __contains__(self, idx: str) -> bool:  # pragma: no cover # no logic
         return idx in self.backend
 
-    def __len__(self) -> int:
+    def __len__(self) -> int:  # pragma: no cover # no logic
         return len(self.backend)
 
     def get(self, idx: str, default=None):