How to get USDC balance of impersonated wallet in Hardhat test

Question

I am writing a smart contract that uses USDC when a NFT is purchased (so the USDC is transferred from the seller to the buyer).

I am trying to test it in Hardhat but I am having troubles when using USDC on my hardhat tests. I forked the goerli testnet and impersonated by wallet has it has USDC in goerli.

When I do an NFT purchase with my account, it revert with an error "ERC20: transfer amount exceeds balance" so I am trying to display the USDC balance to understand where the problem is, but the USDC balance is returning 0, when I have in my account USDC.

What am I missing?

This is my solidity function:

     function createMarketSale(uint256 tokenId)
        public
    {
        uint priceUSD = idToMarketItem[tokenId].priceUSD;
        address seller = idToMarketItem[tokenId].seller;

      
        USDc.transfer(seller, priceUSD * 10 ** 6);
      
        _transfer(idToMarketItem[tokenId].owner, msg.sender, tokenId);

        idToMarketItem[tokenId].owner = msg.sender;
        idToMarketItem[tokenId].sold = true;
        _itemsSold.increment();
    }

This is my hardhat test:

const USDC_ADDRESS = "0x98339D8C260052B7ad81c28c16C0b98420f2B46a";
const USDC_WHALE = "0x682...";
const ERC20ABI = require('./ERC20.json');

beforeEach(async () => {
    [owner, addr1, addr2] = await ethers.getSigners();

    const ArtworkContract = await ethers.getContractFactory("Artwork");
    artworkcontract = await ArtworkContract.deploy();


    // This should send USDC to addr1 but addr1 is not receiving USDC (or I cannot see it!)
    await impersonateFundErc20(
      USDC_ADDRESS,
      USDC_WHALE,
      addr1,
      "50.0",
      6
    );
  }) 

  describe("MarketPlace", () => {

    it("Should create an NFT", async function () {
      const [owner, addr1, addr2] = await ethers.getSigners();
      const whaleAddress = await ethers.getSigner(USDC_WHALE);
      
      await artworkcontract.deployed();
  
      await owner.sendTransaction({
        to: whaleAddress.address,
        value: ethers.utils.parseEther("1000.0"), // Send more ether to impersonated account
      });

      const USDC = new ethers.Contract(USDC_ADDRESS, ERC20ABI, ethers.provider);
      USDCBalance = await USDC.balanceOf(USDC_WHALE);
      console.log("USDCBalance: " + USDCBalance); // This is returning 0

      await artworkcontract.connect(addr1).createToken("uri1","url1",2)
      const allItems = await artworkcontract.fetchAllItems()
      console.log("allItems:",allItems)
  
      const ETHBalance = await ethers.provider.getBalance(USDC_WHALE);
      console.log("ETHBalance: ",ETHBalance);
  
      await artworkcontract.connect(whaleAddress).createMarketSale(1) // reverts with error ERC20: transfer amount exceeds balance

    });

Answer 1

First you have to approve the USDC amount on the USDC contract from the senders wallet on the frontend. Then you can call this createMarketSale function on your contract that will transfer the USDC from the sender to your contract and then to the seller from your contract.

function createMarketSale(uint256 tokenId) public {
   uint256 priceUSD = idToMarketItem[tokenId].priceUSD;
   address seller = idToMarketItem[tokenId].seller;
   // transfer amount from buyer to contract
   USDc.transferFrom(msg.sender, address(this), priceUSD * 10**6);
   // then send from the contract to seller
   USDc.transfer(seller, priceUSD * 10**6);

   _transfer(idToMarketItem[tokenId].owner, msg.sender, tokenId);

   idToMarketItem[tokenId].owner = msg.sender;
   idToMarketItem[tokenId].sold = true;
   _itemsSold.increment();
}