function isValidBuyer(uint256 buyTokenQty, uint256 senderValue) public  constant returns (bool)
    {
        if(!isUserExist(msg.sender))
        {
            msg.sender.transfer(senderValue); //Refund Ether
            return false ;
        }
        else
        {
            return true ;
        }
    }

it('TCC001: should check invalid buyer and should return false',   async () => {
let tempRes1=await instChain.isValidBuyer(100,1,{from:account2,gas:'220000'});

 assert.isTrue(!tempRes1);
});