Unable to transfer ether to a contract from a account in truffle. Getting Exception VM Exception while processing transaction: invalid opcode

Question

I am trying to simulate send ether fail in KingOfEther contract: The contract is specified below.

contract KingOfEther {
    address public king;
    uint public claimPrice = 20;
    address owner;

    function KingOfEther() {
        owner = msg.sender;
        king = msg.sender;
    }
    function ()
    {

    }
    function claimthrone(uint amount)  {
        if (amount < claimPrice) throw;
        uint value_paid=amount;
        uint compensation =value_paid-claimPrice;
        if(!king.send(compensation))
          throw;
        king = msg.sender;
        claimPrice = value_paid;
    }
    /* other functions below */
    /*function calculateCompensation() returns (uint){
        return 0;
    }
    function calculateNewPrice() returns (uint){
        return 0;
    }*/
}

In test folder of truffle i have added the following test, not complete but just trying to interact with testrpc:

var KingOfEther = artifacts.require("./KingOfEther.sol");

contract("KingOfEtherContract",function(accounts){
   it("first test", function(){
      return KingOfEther.deployed().then(function(instance){
      var koet=instance;
      var account_two=accounts[1];
      var account_one=accounts[0];
      //console.log(KingOfEther.deployed());
      return koet.king.call().then(function(val) {
        console.log(val);
        console.log(account_one);
        console.log(web3.fromWei(web3.eth.getBalance(account_one).toNumber()));
        console.log(web3.fromWei(web3.eth.getBalance(account_two).toNumber()));
          console.log(web3.fromWei(web3.eth.getBalance(val).toNumber()));



        return koet.claimthrone(22,{from:account_two});
      }).then(function(x){
        return koet.king.call().then(function(val) {

          console.log(web3.fromWei(web3.eth.getBalance(val).toNumber()));
          console.log(web3.fromWei(web3.eth.getBalance(account_one).toNumber()));
          console.log(web3.fromWei(web3.eth.getBalance(account_two).toNumber()));
        });
      });

    });});});

On executing i am getting exception on send call.

Contract: KingOfEtherContract first test:
     Error: VM Exception while processing transaction: invalid opcode
      at Object.InvalidResponse (/home/utkarash/.nvm/versions/node/v8.2.1/lib/node_modules/truffle/build/cli.bundled.js:37295:16)
      at /home/utkarash/.nvm/versions/node/v8.2.1/lib/node_modules/truffle/build/cli.bundled.js:224765:36
      at /home/utkarash/.nvm/versions/node/v8.2.1/lib/node_modules/truffle/build/cli.bundled.js:208348:9
      at XMLHttpRequest.request.onreadystatechange (/home/utkarash/.nvm/versions/node/v8.2.1/lib/node_modules/truffle/build/cli.bundled.js:209773:13)
      at XMLHttpRequestEventTarget.dispatchEvent (/home/utkarash/.nvm/versions/node/v8.2.1/lib/node_modules/truffle/build/cli.bundled.js:67130:18)
      at XMLHttpRequest._setReadyState (/home/utkarash/.nvm/versions/node/v8.2.1/lib/node_modules/truffle/build/cli.bundled.js:67420:12)
      at XMLHttpRequest._onHttpResponseEnd (/home/utkarash/.nvm/versions/node/v8.2.1/lib/node_modules/truffle/build/cli.bundled.js:67575:12)
      at IncomingMessage.<anonymous> (/home/utkarash/.nvm/versions/node/v8.2.1/lib/node_modules/truffle/build/cli.bundled.js:67535:24)

Can anyone please help where i am doing wrong? Thanks in advance

Answer 1

Is that because:

uint compensation =value_paid-claimPrice;

and since value_paid < claimPrice, so compensation would be a very large number (as it is uint, "overflow"). And contract doesn't have so high balance, so send() returns false and triggers throw().