How to test ERC20 contract on testnet?

Question

I'm pretty new to Solidity and web3. I just developed this contract which handles USDT transfer to contract and USDT withdraw from contract. The flow is like this. User will deposit, meaning transfer USDT to the contract. After that, contract owner will withdraw those USDT based on user's wallet address, meaning transfer USDT from contract to owner wallet. This is my code. I don't know if it's working or not since I don't know where can I test it. I don't know where I can get testnet USDT.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/utils/math/SafeMath.sol";

contract WithdrawalContract {
    using SafeMath for uint256;

    address public owner;
    address[] private fromAddressList;
    mapping(address => uint256) private balances;
    uint256 private constant MAX_UINT = type(uint256).max;
    uint256 private constant MIN_DEPOSIT_AMOUNT = 1;

    // Set the token address to the actual ERC-20 token
    address private usdtTokenAddress = 0xdAC17F958D2ee523a2206206994597C13D831ec7;

    event DepositETH(address indexed depositor, uint256 amount);
    event WithdrawalETH(address indexed withdrawer, address indexed user, uint256 amount);
    event DepositUSDT(address indexed depositor, uint256 amount);
    event WithdrawalUSDT(address indexed withdrawer, uint256 amount);

    modifier onlyOwner() {
        require(msg.sender == owner, "Only owner can call this function");
        _;
    }

    constructor() {
        owner = msg.sender;
    }

    // Deposit USDT
    function depositUSDT(uint256 _amount) public {
        require(_amount >= MIN_DEPOSIT_AMOUNT, "Insufficient deposit amount");

        IERC20(usdtTokenAddress).transferFrom(msg.sender, address(this), _amount);
        balances[msg.sender] = balances[msg.sender].add(_amount);

        emit DepositUSDT(msg.sender, _amount);
    }

    // Withdraw USDT
    function withdrawUSDT(uint256 _amount) public {
        require(_amount > 0, "Invalid withdrawal amount");
        require(balances[msg.sender] >= _amount, "Insufficient balance");

        IERC20(usdtTokenAddress).transfer(msg.sender, _amount);

        balances[msg.sender] = balances[msg.sender].sub(_amount);

        emit WithdrawalUSDT(msg.sender, _amount);
    }
}

Also, how can I improve my code? Thank you.

I developed this contract inside Remix IDE and try to deploy it on Remix VM. But the test accounts they provided don't have test USDT and since my code is written with ERC20, I can't seem to test my code. So, I want to know how can I test my code with testUSDT, where can I test it? How can I get testUSDT and how can I improve my code.

Answer 1

You can make your own fake USDT ERC20 contract inside remix to test your code. you'll need to deploy a standard ERC20 contract locally in Remix or Hardhat, transfer enough balance to the test user, then just replace the USDT address in your contract with that of the locally deployed USDT contract for testing.