How to write smart contract tests in Hardhat?

Hardhat provides a powerful testing framework based on Mocha and Chai. Here are the core points for writing tests:

Test File Structure:

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

describe("MyContract", function () {
  beforeEach(async function () {
    const MyContract = await ethers.getContractFactory("MyContract");
    this.contract = await MyContract.deploy();
    await this.contract.deployed();
  });

  it("should return the correct value", async function () {
    expect(await this.contract.getValue()).to.equal(42);
  });
});

Core Features:

1. Contract Deployment

javascript
const Contract = await ethers.getContractFactory("ContractName");
const contract = await Contract.deploy();
await contract.deployed();

1. Function Calls and Assertions

javascript
const tx = await contract.someFunction(param1, param2);
await tx.wait(); // Wait for transaction confirmation
expect(await contract.someViewFunction()).to.equal(expectedValue);

1. Event Listening

javascript
await expect(contract.someFunction())
  .to.emit(contract, "EventName")
  .withArgs(arg1, arg2);

1. Transaction Revert Testing

javascript
await expect(contract.failingFunction())
  .to.be.revertedWith("Error message");

1. Snapshot Functionality

javascript
const snapshot = await ethers.provider.send("evm_snapshot", []);
// Perform some operations
await ethers.provider.send("evm_revert", [snapshot]);

1. Time Manipulation

javascript
await ethers.provider.send("evm_increaseTime", [3600]); // Increase by 1 hour
await ethers.provider.send("evm_mine"); // Mine new block

Best Practices:

• Use beforeEach and afterEach to manage test state
• Provide clear descriptions for each test case
• Test both normal and exception paths
• Use meaningful test data
• Maintain test independence and reproducibility