@Override
    public RelOptCost computeSelfCost(RelOptPlanner relOptPlanner, RelMetadataQuery relMetadataQuery) {
      return null;
    }
Functional and parallel execution tests for {@link MaterializedViewsCache}.
Parallel execution test is disabled by default.
ql/src/test/org/apache/hadoop/hive/ql/metadata/TestMaterializedViewsCache.java