Lesson 12: The test is not returning the value I expected, why is this happening?

[cipher222]

I was writing some of my own tests for the openzepplin ERC20 contract and this is happening. I think I am missing something because the math is not adding up. Could someone please explain why this is happening? My thought process writing my test is explained in more detail below https://github.com/smartcontractkit/full-blockchain-solidity-course-js/discussions/1378#discussioncomment-3284336

const { expect } = require("chai")
const { deployments, ethers, getNamedAccounts } = require("hardhat")
const {
  ContractType,
} = require("hardhat/internal/hardhat-network/stack-traces/model")

describe("Raffle Unit Tests", function () {
  /* allowances testing
    should approve other address to spend token
    does not allow an unnaproved address to do transfers
    emits an aproval event
    the allowance being set is accurate
    does not let the user spend more than their allowance
    */
  let deployer, user1, user2, ourToken //global vars
  beforeEach(async () => {
    //const accounts = await ethers.getSigners() //gets the account specified for the network in hardhat config
    // const deployer = accounts[0]
    // const testAccount = accounts[1]
    // accounts = await ethers.getSigners() (the other way to do this is specified below)
    const accounts = await getNamedAccounts()
    deployer = accounts.deployer
    user1 = accounts.user1
    user2 = accounts.user2
    // deployer + user1 are abstracted from the namedAccounts object. getNamedAccounts gets these objects for us
    //this could also be writen as const {deployer} = await getNamedAccounts but we want to set a global var
    await deployments.fixture(["all"])
    ourToken = await ethers.getContract("OurToken", deployer) //gets the most recent deployment of whatever contract specified
    //whenever we call a function in will automaticaly be from that deployer account
  })

  it("spender should be allowed to use its allowance and its allowance is subtracted", async () => {
    const allowance = ethers.utils.parseEther("5")
    const tokensToSpend = ethers.utils.parseEther("4")
    const expectedNum = ethers.utils.parseEther("1")

    await ourToken.approve(user1, allowance) //give user1 5 tokens

    const ourToken1 = await ethers.getContract("OurToken", user1) //connect to user1

    await ourToken1.transferFrom(deployer, user2, tokensToSpend) //user1 sends 4 of its allowance tokens owned by deployer to user2

    expect(await ourToken1.balanceOf(user2)).to.equal(tokensToSpend)
    expect(await ourToken1.balanceOf(user1)).to.equal(expectedNum)

    // it("does not allow an unnaproved address to do transfers", async function () {})
    // it("emits an approval event", async function () {})
    // it("sets the allowance correctly", async function () {})
    // it("does not let the user spend more than their allowance")
  })
})

The test failure reads this...

 Raffle Unit Tests
    1) spender should be allowed to use its allowance and its allowance is subtracted


  0 passing (2s)
  1 failing

  1) Raffle Unit Tests
       spender should be allowed to use its allowance and its allowance is subtracted:

      AssertionError: Expected "4000000000000000000" to be equal 1000000000000000000
      + expected - actual

       {
      -  "_hex": "0x0de0b6b3a7640000"
      +  "_hex": "0x3782dace9d900000"
         "_isBigNumber": true
       }

[technophile-04]

Hii, Why are you expecting that user1's balance should change? because user1's balance is never changed...At line 36 we have just approved user1 to spend 5 tokens of deployer we haven't transferred it to user1...

[cipher222]

I expected user1’s balance to change because calling approve

function approve(address spender, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, amount);
        return true;
    }

calls the function _approve passing the owner, spender, and amount that are then added to the nested mapping as seen below

function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

When I called tranferFrom (when connected to the contract using user1) I expected _spendAllowance to be called which would transfer money from the spender who is user1 (msg.sender). This is where I believe I might misunderstand the code present.

function transferFrom(
        address from,
        address to,
        uint256 amount
    ) public virtual override returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, amount);
        _transfer(from, to, amount);
        return true;
    }

Finally, after _spendAllowance is called with the parameters (deployer, user1, user2) I expected exactly what I wrote in the test above.

Here is the spendAllowance function where the amount transferred (tokensToSpend = 4) is subtracted from user1’s allowance (allowance = 5) that was approved by the deployer. Then it would reason that 5 - 4 = 1 but somehow user1’s balance is 4 which means that 1 token was taken from the allowance but the other requested 3 were not. This is why I am so confused and was wondering if anyone more adept at reading code might be able to explain what I am missing here. Thanks!

function _spendAllowance(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= amount, "ERC20: insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - amount);
            }
        }
    }

[alymurtazamemon]

@cipher222 Please follow these guidelines next time when you ask a question. How to Ask Question Guide

[cipher222]

I will change it. Sorry

[krakxn]

@cipher222 Make a repo and link it here

[cipher222]

Here is a repo I made https://github.com/cipher222/ERC20-token