public static HazelcastSqlOperatorTable instance() {
        return INSTANCE;
    }
@Test
    public void testReturnTypeInference() {
        for (SqlOperator operator : HazelcastSqlOperatorTable.instance().getOperatorList()) {
            if (operator instanceof HazelcastTableFunction
                    || operator == HazelcastSqlOperatorTable.IN
                    || operator == HazelcastSqlOperatorTable.NOT_IN
                    || operator == HazelcastSqlOperatorTable.UNION
                    || operator == HazelcastSqlOperatorTable.UNION_ALL
                    || operator == HazelcastSqlOperatorTable.ARGUMENT_ASSIGNMENT
                    || operator == HazelcastSqlOperatorTable.DOT) {
                continue;
            }
            boolean valid = operator.getReturnTypeInference() instanceof HazelcastReturnTypeInference;

            assertTrue("Operator must have " + HazelcastReturnTypeInference.class.getSimpleName() + ": " + operator.getClass().getSimpleName(), valid);
        }
    }