function endSale() public {
     require(msg.sender == admin);
     require(tokenContract.transfer(admin,tokenContract.balanceOf(this)));
     selfdestruct(admin);
    }

it('ends token sale', function() {
   `enter preformatted text here` return DappToken.deployed().then(function(instance) {
      // Grab token instance first
      tokenInstance = instance;
      return DappTokenSale.deployed();
    }).then(function(instance) {
      // Then grab token sale instance
      tokenSaleInstance = instance;
      // Try to end sale from account other than the admin
      return tokenSaleInstance.endSale({ from: buyer });
    }).then(assert.fail).catch(function(error) {
      assert(error.message.indexOf('revert' >= 0, 'must be admin to end sale'));
      // End sale as admin
      return tokenSaleInstance.endSale({ from: admin });
    }).then(function(receipt) {
      return tokenInstance.balanceOf(admin);
    }).then(function(balance) {
      assert.equal(balance.toNumber(), 999990, 'returns all unsold dapp tokens to admin');
      // Check that token price was reset when selfDestruct was called
      return tokenSaleInstance.tokenPrice();
    }).then(function(price) {
      assert.equal(price.toNumber(), 0, 'token price was reset');
    });
  });

Error: Attempting to run transaction which calls a contract function, but recipient address 0x970c30c59d21df9fe660a266faf2ba0871dc25ad is not a contract address

 at Object.InvalidResponse (/home/anupam/.config/yarn/global/node_modules/truffle/build/webpack:/~/web3/lib/web3/errors.js:38:1)
      at /home/anupam/.config/yarn/global/node_modules/truffle/build/webpack:/~/web3/lib/web3/requestmanager.js:86:1
      at /home/anupam/.config/yarn/global/node_modules/truffle/build/webpack:/~/truffle-provider/wrapper.js:134:1
      at XMLHttpRequest.request.onreadystatechange (/home/anupam/.config/yarn/global/node_modules/truffle/build/webpack:/~/web3/lib/web3/httpprovider.js:128:1)
      at XMLHttpRequestEventTarget.dispatchEvent (/home/anupam/.config/yarn/global/node_modules/truffle/build/webpack:/~/xhr2/lib/xhr2.js:64:1)
      at XMLHttpRequest._setReadyState (/home/anupam/.config/yarn/global/node_modules/truffle/build/webpack:/~/xhr2/lib/xhr2.js:354:1)
      at XMLHttpRequest._onHttpResponseEnd (/home/anupam/.config/yarn/global/node_modules/truffle/build/webpack:/~/xhr2/lib/xhr2.js:509:1)
      at IncomingMessage.<anonymous> (/home/anupam/.config/yarn/global/node_modules/truffle/build/webpack:/~/xhr2/lib/xhr2.js:469:1)
      at endReadableNT (_stream_readable.js:1064:12)
      at _combinedTickCallback (internal/process/next_tick.js:138:11)
      at process._tickCallback (internal/process/next_tick.js:180:9)