Add an assert to the test

Author: Fokko

tests/integration/test_writes/test_writes.py

@@ -1786,10 +1786,14 @@ def test_double_commit_transaction(
     identifier = "default.arrow_data_files"
     tbl = _create_table(session_catalog, identifier, {"format-version": format_version}, [])
 
+    assert len(tbl.metadata.metadata_log) == 0
+
     with tbl.transaction() as tx:
         tx.append(arrow_table_with_null)
         tx.commit_transaction()
 
+    assert len(tbl.metadata.metadata_log) == 1
+
 
 @pytest.mark.integration
 @pytest.mark.parametrize("format_version", [1, 2])