Fix backend comparison

tests/test_dataset.py

@@ -72,7 +72,9 @@ def test_dataset(audb_cache, tmpdir, repository, db, request):
     assert dataset.version == pytest.VERSION
     assert dataset.repository_object == repository
     with backend_interface.backend:
-        assert dataset.backend == backend_interface
+        # Compare only string,
+        # as backends are not identical
+        assert str(dataset.backend) == str(backend_interface)
     expected_header = audb.info.header(
         db.name,
         version=pytest.VERSION,
@@ -431,7 +433,9 @@ def test_dataset_cache_loading(audb_cache, tmpdir, repository, db, request):
             load_tables=True,
             cache_root=audb_cache,
         )
-        assert dataset.backend == backend_interface
+        # Compare only string representation,
+        # as objects are not identical
+        assert str(dataset.backend) == str(backend_interface)
         assert dataset.deps == deps
         # The dataset header is a not fully loaded `audformat.Database` object,
         # so we cannot directly use `audformat.Database.__eq__()`