Now that we have ERC-20 in our codebase, lets extend it to create our own ERC-20 contract

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

import "forge-std/Script.sol";
import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract MyToken is ERC20 {
    uint256 public number;

    constructor() ERC20("MyToken", "MTK") {}
    function mint(address to, uint256 amount) public {
        _mint(to, amount);
    }
}

Positive tests

Add tests for the standard functions in an ERC-20 contract

1. test minting
2. Test transfers
3. Test approvals

<aside> 💡

You need to learn about some cheat codes in forge before you attempt this assignment. Ref - https://book.getfoundry.sh/forge/cheatcodes (read about pranks)

</aside>

• Solution

Negative tests

Add tests that expect failures

1. User tries to spend tokens they dont have
2. User tries to spend on someone elses behalf what they dont have

• Solution

Class tests

// SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.13;

import "forge-std/Test.sol";

import "src/KiratCoin.sol";

contract TestKiratCoin is Test {

    KiratCoin c;

    function setUp() public {
        c = new KiratCoin();
    }

    function testMint() public {
        c.mint(address(this), 100);
        assertEq(c.balanceOf(address(this)), 100 ,"ok");
        assertEq(c.balanceOf(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f), uint256(0) ,"ok");

        c.mint(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f, 100);
        assertEq(c.balanceOf(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f), 100, "ok");
    }

    function testTransfer() public {
        c.mint(address(this), 100);
        c.transfer(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f, 50);
        
        assertEq(c.balanceOf(address(this)), 50);
        assertEq(c.balanceOf(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f), 50);

        vm.prank(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f);
        c.transfer(address(this), 50);

        assertEq(c.balanceOf(address(this)), 100);
        assertEq(c.balanceOf(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f), 0);
    }

    function testApprovals() public {
        c.mint(address(this), 100);

        c.approve(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f, 10);

        assertEq(c.allowance(address(this), 0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f), 10);
        assertEq(c.allowance(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f, address(this)), 0);
        
        vm.prank(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f);
        c.transferFrom(address(this), 0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f, 5);

        assertEq(c.balanceOf(address(this)), 95, "ok");
        assertEq(c.balanceOf(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f), 5, "ok");
        assertEq(c.allowance(address(this), 0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f), 5);
    }

    function testFailApprovals() public {
        c.mint(address(this), 100);
        c.approve(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f, 10);
        
        vm.prank(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f);
        c.transferFrom(address(this), 0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f, 100);
    }

    function testFailTransfer() public {
        c.mint(address(this), 20);
        c.transfer(0x587EFaEe4f308aB2795ca35A27Dff8c1dfAF9e3f, 100);
    }

}