Uncodemy Blockchain Course: Everything You Need to Know

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

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

/// @title SimpleToken
/// @notice An ERC-20 token built using OpenZeppelin contracts
/// @dev This is what you build in weeks 5–8 of the course
contract SimpleToken is ERC20, Ownable {
    uint256 public constant MAX_SUPPLY = 1_000_000 * 10**18;

    constructor() ERC20("SimpleToken", "SMPL") Ownable(msg.sender) {
        _mint(msg.sender, MAX_SUPPLY);
    }

    /// @notice Allow the owner to mint more tokens (bounded by MAX_SUPPLY)
    function mint(address to, uint256 amount) external onlyOwner {
        require(totalSupply() + amount <= MAX_SUPPLY, "Exceeds max supply");
        _mint(to, amount);
    }

    /// @notice Burn tokens from the caller's balance
    function burn(uint256 amount) external {
        _burn(msg.sender, amount);
    }
}

// Real skills you learn:
// - ERC-20 standard (fungible tokens)
// - OpenZeppelin library patterns
// - Access control (onlyOwner)
// - Supply caps + minting/burning logic
// - Events (via ERC20 base contract)
//
// In week 8, you extend this to include:
// - Pausable transfers
// - Snapshot functionality
// - Governance voting (ERC20Votes)

// test/SimpleToken.test.js
// Real Hardhat tests — the way professional smart contract developers test code
// You write these in weeks 7–10

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

describe("SimpleToken", function () {
  let token, owner, addr1, addr2;

  beforeEach(async function () {
    [owner, addr1, addr2] = await ethers.getSigners();
    const SimpleToken = await ethers.getContractFactory("SimpleToken");
    token = await SimpleToken.deploy();
    await token.waitForDeployment();
  });

  it("mints max supply to the deployer", async function () {
    const ownerBalance = await token.balanceOf(owner.address);
    expect(ownerBalance).to.equal(1_000_000n * 10n ** 18n);
  });

  it("allows transfers between accounts", async function () {
    await token.transfer(addr1.address, ethers.parseEther("1000"));
    expect(await token.balanceOf(addr1.address)).to.equal(ethers.parseEther("1000"));
  });

  it("prevents non-owners from minting", async function () {
    await expect(
      token.connect(addr1).mint(addr1.address, ethers.parseEther("1"))
    ).to.be.revertedWithCustomError(token, "OwnableUnauthorizedAccount");
  });

  it("burns tokens from the caller's balance", async function () {
    await token.transfer(addr1.address, ethers.parseEther("1000"));
    await token.connect(addr1).burn(ethers.parseEther("500"));
    expect(await token.balanceOf(addr1.address)).to.equal(ethers.parseEther("500"));
  });
});

// Real skills demonstrated:
// - Hardhat testing framework (the standard for Solidity)
// - Assertion patterns (chai)
// - Testing access control (reverts)
// - Testing state changes (balances)
//
// Every production smart contract needs this level of testing —
// because once deployed, bugs mean real money lost.