Hardhat testing setup in Blockchain / Solidity

Introduction

Hardhat testing setup helps you check if your smart contracts work correctly before using them on real blockchains. It saves time and money by catching mistakes early.

When you want to make sure your smart contract functions as expected.

Before deploying contracts to a live blockchain to avoid costly errors.

When you want to automate contract checks during development.

To test how contracts behave with different inputs and scenarios.

When collaborating with others to ensure consistent contract behavior.

Syntax

Blockchain / Solidity

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

describe("ContractName", function () {
  it("should do something", async function () {
    const Contract = await ethers.getContractFactory("ContractName");
    const contract = await Contract.deploy();
    await contract.deployed();

    expect(await contract.someFunction()).to.equal(expectedValue);
  });
});

describe groups tests together.

it defines a single test case.

Examples

This example tests storing and retrieving a number in a contract.

Blockchain / Solidity

describe("SimpleStorage", function () {
  it("should store and retrieve a value", async function () {
    const SimpleStorage = await ethers.getContractFactory("SimpleStorage");
    const storage = await SimpleStorage.deploy();
    await storage.deployed();

    await storage.store(42);
    expect(await storage.retrieve()).to.equal(42);
  });
});

This test checks if the token contract assigns the initial supply to the owner.

Blockchain / Solidity

describe("Token", function () {
  it("should assign initial supply to owner", async function () {
    const [owner] = await ethers.getSigners();
    const Token = await ethers.getContractFactory("Token");
    const token = await Token.deploy(1000);
    await token.deployed();

    expect(await token.balanceOf(owner.address)).to.equal(1000);
  });
});

Sample Program

This test deploys a Counter contract, checks the initial count is zero, then increments and checks the count is one.

Blockchain / Solidity

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

describe("Counter", function () {
  it("should start at zero and increment", async function () {
    const Counter = await ethers.getContractFactory("Counter");
    const counter = await Counter.deploy();
    await counter.deployed();

    expect(await counter.getCount()).to.equal(0);

    await counter.increment();
    expect(await counter.getCount()).to.equal(1);
  });
});

Important Notes

Make sure your contract is compiled before running tests.

Use npx hardhat test to run tests in your project folder.

Tests run on a local blockchain provided by Hardhat automatically.

Summary

Hardhat testing setup helps you write and run tests for smart contracts easily.

Use describe and it blocks to organize tests.

Tests run on a local blockchain, so no real money is used.

Practice

1. What is the main purpose of using Hardhat testing setup in blockchain development?

easy

A. To create user interfaces for blockchain applications

B. To deploy smart contracts directly to the main Ethereum network

C. To write and run tests for smart contracts on a local blockchain

D. To mine real cryptocurrency coins

Solution

1. Step 1: Understand Hardhat testing role

   Hardhat testing setup is designed to help developers write and run tests for smart contracts safely.

2. Step 2: Identify the environment used

   Tests run on a local blockchain, which means no real money or main network is involved.

3. Final Answer:

   To write and run tests for smart contracts on a local blockchain -> Option C

4. Quick Check:

   Hardhat testing = local smart contract tests [OK]

Hint: Hardhat tests run locally, not on mainnet [OK]

Common Mistakes:

• Confusing testing with deployment to mainnet
• Thinking Hardhat mines real coins
• Assuming Hardhat builds user interfaces

2. Which of the following is the correct way to start a test suite in Hardhat using Mocha?

easy

A. test('MyContract', function() { ... })

B. describe('MyContract', function() { ... })

C. suite('MyContract', () => { ... })

D. context('MyContract', function() { ... })

Solution

1. Step 1: Recall Mocha test structure

   Hardhat uses Mocha for testing, which organizes tests with describe blocks.

2. Step 2: Identify correct syntax

   The describe function takes a string and a callback function to group tests.

3. Final Answer:

   describe('MyContract', function() { ... }) -> Option B

4. Quick Check:

   Mocha test suites use describe() [OK]

Hint: Use describe() to group tests in Hardhat [OK]

Common Mistakes:

• Using test() instead of describe() for suites
• Confusing suite() or context() with Mocha syntax
• Missing function keyword or arrow function

3. Given this Hardhat test snippet, what will be the output when running the test?

describe('SimpleTest', function() {
  it('should return true', async function() {
    const result = true;
    console.log(result);
    expect(result).to.equal(true);
  });
});

medium

A. true and test passes

B. false and test fails

C. undefined and test passes

D. Error: expect is not defined

Solution

1. Step 1: Analyze console output

   The code logs the variable result which is set to true, so console shows 'true'.

2. Step 2: Check assertion

   The test asserts result equals true, which is correct, so test passes.

3. Final Answer:

   true and test passes -> Option A

4. Quick Check:

   console.log(true) + expect(true) passes [OK]

Hint: Check console.log and expect values carefully [OK]

Common Mistakes:

• Assuming expect is undefined without import
• Confusing console output with test result
• Thinking test fails because of async function

4. Identify the error in this Hardhat test code snippet:

describe('Token', function() {
  it('should deploy contract', async () => {
    this.timeout(20000);
    const Token = await ethers.getContractFactory('Token');
    const token = await Token.deploy();
    await token.waitForDeployment();
    expect(token.address).to.be.a('string');
  });
});

medium

A. Missing import of ethers from Hardhat

B. deploy() should not be awaited

C. Incorrect assertion method for address type

D. Using arrow function in it() causes context loss

Solution

1. Step 1: Check function style in it()

   Using arrow functions in Mocha's it blocks can cause loss of this context, which Hardhat sometimes relies on.

2. Step 2: Verify other parts

   Imports and await usage are correct; assertion syntax is valid for checking string type.

3. Final Answer:

   Using arrow function in it() causes context loss -> Option D

4. Quick Check:

   Use function() not arrow in it() [OK]

Hint: Avoid arrow functions in it() blocks [OK]

Common Mistakes:

• Ignoring context loss with arrow functions
• Thinking deploy() is synchronous
• Assuming ethers import is automatic

5. You want to test a smart contract function that transfers tokens and emits an event. Which setup correctly tests the event emission using Hardhat and Chai?

hard

A. await expect(token.transfer(addr1.address, 100)).to.emit(token, 'Transfer').withArgs(owner.address, addr1.address, 100);

B. expect(token.transfer(addr1.address, 100)).to.emit('Transfer').withArgs(owner.address, addr1.address, 100);

C. await token.transfer(addr1.address, 100); expect(token).to.emit('Transfer');

D. token.transfer(addr1.address, 100); expect(token).to.emit(token, 'Transfer');

Solution

1. Step 1: Understand event testing syntax

   Hardhat with Chai uses await expect(transaction).to.emit(contract, eventName).withArgs(...) to test events.

2. Step 2: Check options for correct usage

   await expect(token.transfer(addr1.address, 100)).to.emit(token, 'Transfer').withArgs(owner.address, addr1.address, 100); correctly awaits the transaction and specifies contract and event with arguments.

3. Step 3: Identify errors in other options

   The other options either miss the await before expect, fail to specify the contract instance in to.emit(), or use incorrect syntax chaining.

4. Final Answer:

   await expect(token.transfer(addr1.address, 100)).to.emit(token, 'Transfer').withArgs(owner.address, addr1.address, 100); -> Option A

5. Quick Check:

   Use await expect(...).to.emit(contract, event) [OK]

Hint: Always await expect() when testing events [OK]

Common Mistakes:

• Forgetting to await the expect call
• Not specifying the contract in to.emit()
• Calling expect on transaction result instead of promise