I am trying to write test for erc20 token and when I try to revert the transaction if the sender has insufficient balance, it is throwing an error.

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Solidity code for transfer function

  function _transfer(address _from, address _to, uint256 _amount) internal {
    require(balanceOf[_from] >= _amount);
    require(balanceOf[_to] + _amount >= balanceOf[_to]);
    balanceOf[_to] += _amount;
    balanceOf[_from] -= _amount;
    emit Transfer(_from, _to, _amount);
  function transfer(address _to, uint256 _amount) public returns(bool) {
    require(msg.sender != address(0) && _to != address(0), "Address cannot be zero");
    _transfer(msg.sender, _to, _amount);
    return true;

And the code for test:

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

describe("Blue20", () => {
  let Token, token, owner, addr1, addr2;
  beforeEach(async () => {
    Token = await ethers.getContractFactory("blue20");
    token = await Token.deploy();
    [owner, addr1, addr2, _] = await ethers.getSigners();

  describe("Deployment", () => {
    it("Checking the deployment processs", async () => {
      expect(await token.owner()).to.equal(owner.address);

    it("Should assign the total tokens to the owner", async () => {
      const ownerBalance = await token.balance(owner.address);
      expect(await token.totalSupply()).to.equal(ownerBalance);

  describe("Transactions", () => {
    it("Succesfully transfer the tokens and verify", async () => {
      await token.transfer(addr1.address, 100);
      let addr1Balance = await token.balance(addr1.address);
      expect(await addr1Balance).to.equal(100);

      await token.connect(addr1).transfer(addr2.address, 100);
      let addr2Balance = await token.balance(addr2.address);

    it("Should fail if sender doesn't have enough tokens", async () => {
        await token.connect(addr1).transfer(owner.address, 1)
      ).to.be.revertedWith("Not enough Tokens");

I use hardhat as development environment.

  • Just adding for reffernce but you can also get this error from provider/hardhat if the gas price you set is too high or too low. at the time of writing 5 gwei seems about right
    – Alex_Nabu
    Commented May 30, 2023 at 0:19

2 Answers 2


A couple of things you should change in your test. First the await keyword should be outside the expect. Secondly, for getting the address from signers, you should use getAddress(). Try changing your test to:

it("Should fail if sender doesn't have enough tokens", async () => {
  await expect(token.connect(addr1).transfer(owner.getAddress(), 1) ).to.be.revertedWith("Not enough Tokens");
  • why should the await keyword be outside? See the response below your response to understand more.
    – amit
    Commented Feb 20, 2023 at 10:27

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See on line 23 the await keyword is inside, I try to bring it outside it gives me an error even, the vs code says placing the await keyword there won't affect anything.

But again in line 32 if I place the await keyword inside instead of outside it gives an error, why??

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