Function returns undefined

Question

I have a very simple function in my Solidity contract, that I'm trying to test its return value with Hardhat.

    function mintNFT(address _recipient) public returns (uint256)
    {
        uint256 tokenId = calculateTokenID();
        return tokenId;
    }

where tokenId has some logic to generate a uint256. I've added a console.log(tokenId) in the Smart Contract which correctly prints out the tokenId, however, when returned and attempted to test, it comes back as undefined

const { expect } = require('chai');
// Import utilities from Test Helpers
const { BN, expectEvent, expectRevert } = require('@openzeppelin/test-helpers');
// Load compiled artifacts
const CONTRACT = artifacts.require('MyContract');
// Start test block
contract('CONTRACT', function ([ owner, other ]) {
  beforeEach(async function () {
    this.contract = await CONTRACT.new();
    await this.contract.initialize();
  });
it("mintNFT generated a valid token ID", async function () {
    const tokendID = await this.contract.mintNFT();
    expect(tokendID.to.equal(1));
  });

Error:

  1) Contract: DPC
       mintNFT generated a valid token ID:
     TypeError: Cannot read properties of undefined (reading 'equal')
      at Context.<anonymous> (test/DPC_NFT.js:29:24)
      at processTicksAndRejections (node:internal/process/task_queues:96:5)

I've even tried hard-coding the function return to a number, and the test still comes back as undefined. Would greately appreciate your help

not the answer but tx does not return value. So even if it works correctly it will return a tx response and not the token id — Majd TL, Apr 11 '22 at 16:07
How would you go on about testing something like this? i.e. the returned value of a function? — teh0wner, Apr 11 '22 at 17:12
@teh0wner The usual solution is to trigger an event and read the event parameters from the transaction receipt. https://ethereum.stackexchange.com/a/3293/ — Ismael, Apr 12 '22 at 04:53

score 1 · Answer 1 · answered Apr 11 '22 at 16:13

1

you are trying to access to property on tokenID that is wrong try this line :

expect(tokenID).to.equal('value you are expect');

answered Apr 11 '22 at 16:13

Mohammad

106
4

I'm pretty sure that await this.contract.mintNFT(); does not return tokenID, it is a transaction – Majd TL Apr 12 '22 at 14:38

Function returns undefined

1 Answers1