Hardhat testing setup in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Hardhat in blockchain development?

Hardhat is a development environment to compile, deploy, test, and debug Ethereum software. It helps developers write smart contracts and test them locally.

beginner

Which command initializes a new Hardhat project?

The command npx hardhat starts the Hardhat project setup wizard, which helps create the project structure and configuration files.

beginner

What file contains the configuration for Hardhat testing?

The hardhat.config.js file contains settings for the Hardhat environment, including network configurations and plugins for testing.

intermediate

How do you write a simple test in Hardhat using Mocha and Chai?

You write tests inside the test/ folder using JavaScript. Use describe blocks to group tests and it blocks for individual tests. Use expect from Chai to check results.

beginner

What command runs the tests in a Hardhat project?

Use npx hardhat test to run all tests in the test/ directory. This runs your smart contract tests locally.

Which folder typically contains Hardhat test files?

A test/

B src/

C contracts/

D scripts/

Hardhat test files are usually placed in the test/ folder.

What library is commonly used with Hardhat for assertions in tests?

A Lodash

B React

C Express

D Chai

Chai is a popular assertion library used with Hardhat tests.

Which command initializes a Hardhat project?

A hardhat start

B npm install hardhat

C npx hardhat

D node hardhat.js

Running npx hardhat starts the project setup wizard.

What does npx hardhat test do?

A Runs all tests in the test folder

B Compiles smart contracts

C Deploys contracts to mainnet

D Starts a local blockchain node

It runs all the tests written in the test/ directory.

Which file configures Hardhat settings?

A package.json

B hardhat.config.js

C index.js

D truffle-config.js

The hardhat.config.js file holds Hardhat configuration.

Explain the steps to set up a basic Hardhat testing environment from scratch.

Think about commands, folder structure, and test writing.

Describe how you write a simple test for a smart contract function using Hardhat and Chai.

Focus on test structure and assertion.

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