public static HazelcastSqlOperatorTable instance() {
        return INSTANCE;
    }
@Test
    public void testOperandTypeChecker() {
        for (SqlOperator operator : HazelcastSqlOperatorTable.instance().getOperatorList()) {
            boolean valid = operator instanceof HazelcastOperandTypeCheckerAware
                    || operator instanceof HazelcastTableFunction
                    || operator instanceof HazelcastCaseOperator
                    || operator == HazelcastSqlOperatorTable.ARGUMENT_ASSIGNMENT
                    || operator == HazelcastSqlOperatorTable.DOT;

            assertTrue("Operator must implement one of classes from " + HazelcastFunction.class.getPackage().toString()
                    + ": " + operator.getClass().getSimpleName(), valid);
        }
    }