I have created two basic ERC20 tokens (TokenA and TokenB) and a contract that swaps TokenA with TokenB. Everything seems working but I get the error above when I run the test file. How can BigNumber { value: "0" } be different from itself? Can anyone please help?


// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract TokenA is ERC20 {
    constructor() ERC20("TokenA", "TA") {}

    function mint(address to, uint256 amount) public {
        _mint(to, amount);


// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract TokenB is ERC20 {
    constructor() ERC20("TokenB", "TB") {}

    function mint(address to, uint256 amount) public {
        _mint(to, amount);

Swap Contract

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "hardhat/console.sol";

contract SwapAforB {
    uint256 private exchangeRatio;
    ERC20 public TokenA;
    ERC20 public TokenB;

    constructor(uint256 _exchangeRatio, address tokenAAddress, address tokenBAddress) {
        exchangeRatio = _exchangeRatio;
        TokenA = ERC20(tokenAAddress);
        TokenB = ERC20(tokenBAddress);

    function swapTokenAforB(uint256 amount) public {
        //Check balance of TokenA 
        require(TokenA.balanceOf(msg.sender) >= amount, "Insufficient balance of TokenA");
        // Approve swapContract to spend TokenA on behalf of msg.sender
        require(TokenA.allowance(msg.sender, address(this)) >= amount, "TokenA allowance too low");

        // Calculate the amount of TokenB to send
        uint256 amountB = amount / exchangeRatio;

        require(TokenB.balanceOf(address(this)) >= amount, "Exchange has insufficient balance of TokenB");

        // Transfer TokenA from msg.sender to this contract
        require(TokenA.transferFrom(msg.sender, address(this), amount), "TokenA Transfer failed");

        console.log("amountB  ", amountB);
        console.log("TkB Balance ", TokenB.balanceOf(address(this)));

        // Transfer TokenB from this contract to msg.sender
        require(TokenB.transfer(msg.sender, amountB), "TokenB Transfer failed");


const { expect } = require("chai");
const { BigNumber } = require('ethers');

describe("TokenA <-> TokenB Swap", function () {
  let tokenA, tokenB, swapContract;
  let owner, alice;
  const exchangeRatio = 2; 

  beforeEach(async function () {
    // Deploy TokenA and TokenB contracts
    const TokenA = await ethers.getContractFactory("TokenA");
    tokenA = await TokenA.deploy();
    const TokenB = await ethers.getContractFactory("TokenB");
    tokenB = await TokenB.deploy();
    //Deploy swapContract
    const SwapContract = await ethers.getContractFactory("SwapAforB");
    swapContract = await SwapContract.deploy(exchangeRatio, tokenA.address, tokenB.address);

    // Mint initial supply of TokenA and TokenB for Owner
    [owner, alice] = await ethers.getSigners();
    const initialSupply = ethers.utils.parseEther("1000");
    await tokenA.mint(owner.address, initialSupply);
    await tokenB.mint(owner.address, initialSupply);

  it("should swap TokenA for TokenB", async function () {
    // Step 1: Transfer tokenA to Alice and tokenB to swapToken
    const amount = ethers.utils.parseEther("100");
    await tokenA.transfer(alice.address, amount);
    await tokenB.transfer(swapContract.address, amount);

    // Step 2: Alice approves swapContract to transfer TokenA
    await tokenA.connect(alice).approve(swapContract.address, amount);

    // Step 3: Alice swaps TokenA for TokenB
    await swapContract.connect(alice).swapTokenAforB(amount);

    // Check that Alice's balances have been updated correctly
    const balanceA = await tokenA.balanceOf(alice.address);
    const balanceB = await tokenB.balanceOf(alice.address);


1 Answer 1


Object types are being compared by reference, not by content. Like:

let foo = {};
let bar = {};
console.log(foo === bar);
//> false

So, convert to simple types - number, string or bigint

// if your env supports bigints

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