fix: flaky test when sync metadata (#21306)

tests/integration_tests/sqla_models_tests.py

@@ -453,7 +453,8 @@ def test_fetch_metadata_for_updated_virtual_table(self):
 
         # make sure the columns have been mapped properly
         assert len(table.columns) == 4
-        table.fetch_metadata(commit=False)
+        with db.session.no_autoflush:
+            table.fetch_metadata(commit=False)
 
         # assert that the removed column has been dropped and
         # the physical and calculated columns are present
@@ -465,15 +466,13 @@ def test_fetch_metadata_for_updated_virtual_table(self):
         }
         cols: Dict[str, TableColumn] = {col.column_name: col for col in table.columns}
         # assert that the type for intcol has been updated (asserting CI types)
-        backend = get_example_database().backend
+        backend = table.database.backend
         assert VIRTUAL_TABLE_INT_TYPES[backend].match(cols["intcol"].type)
         # assert that the expression has been replaced with the new physical column
         assert cols["mycase"].expression == ""
         assert VIRTUAL_TABLE_STRING_TYPES[backend].match(cols["mycase"].type)
         assert cols["expr"].expression == "case when 1 then 1 else 0 end"
 
-        db.session.delete(table)
-
     @patch("superset.models.core.Database.db_engine_spec", BigQueryEngineSpec)
     def test_labels_expected_on_mutated_query(self):
         query_obj = {