Hardhat testing setup in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Hardhat test snippet?

Consider this simple Hardhat test for a smart contract that stores a number. What will the test output when run?

Blockchain / Solidity

describe('SimpleStorage', function () {
  it('should return the initial value', async function () {
    const SimpleStorage = await ethers.getContractFactory('SimpleStorage');
    const storage = await SimpleStorage.deploy();
    await storage.deployed();

    const value = await storage.retrieve();
    console.log('Stored value:', value.toString());
  });
});

A Stored value: 0

B Stored value: undefined

C Stored value: null

D TypeError: value.toString is not a function

💡 Hint

Think about the default value of a uint256 in Solidity.

The default value of an uninitialized uint256 in Solidity is 0. The retrieve() function returns this value, which is a BigNumber object. Calling toString() converts it to '0'.

🧠 Conceptual

intermediate

Which Hardhat testing setup step is missing here?

You want to write tests for your smart contract using Hardhat. You have installed Hardhat and created a test file. You wrote tests but they fail because ethers is undefined. What step did you miss?

A Importing <code>ethers</code> from Hardhat in the test file

B Installing <code>ethers</code> package separately

C Running <code>npx hardhat compile</code> before tests

D Adding <code>mocha</code> as a dev dependency

💡 Hint

Check how you access Hardhat's built-in libraries in tests.

Hardhat injects ethers into the test environment, but you must import it explicitly in your test file using const { ethers } = require('hardhat'); to use it.

🔧 Debug

advanced

Why does this Hardhat test fail with a timeout?

Look at this test code snippet. The test never finishes and times out. What is the cause?

Blockchain / Solidity

describe('Token', function () {
  it('should mint tokens', async function () {
    const Token = await ethers.getContractFactory('Token');
    const token = await Token.deploy();
    // Missing await here
    await token.deployed();

    const tx = await token.mint(accounts[0].address, 100);
    await tx.wait();

    const balance = await token.balanceOf(accounts[0].address);
    console.log('Balance:', balance.toString());
  });
});

A mint function does not exist on the contract

B tx.wait() is called incorrectly without await

C accounts is not defined, causing a ReferenceError

D Missing await on token.deployed() causes the test to hang

💡 Hint

Check asynchronous calls that might block the test.

The token.deployed() call returns a promise that must be awaited. Without await, the test continues before deployment finishes, causing unpredictable behavior and timeout.

📝 Syntax

advanced

Which option fixes the syntax error in this Hardhat test snippet?

Identify the option that corrects the syntax error in this test code:

describe('MyContract', function() {
  it('does something', async function() {
    const contract = await ethers.getContractFactory('MyContract')
    const instance = await contract.deploy()
    await instance.deployed()

    const result = await instance.myFunction()
    console.log('Result:', result)
  )
})

A Change <code>async function()</code> to <code>async () =></code>

B Add a semicolon after <code>await instance.deployed()</code>

C Replace the closing parenthesis <code>)</code> after <code>console.log</code> with a closing curly brace <code>}</code>

D Add a missing comma after <code>describe</code> function

💡 Hint

Look carefully at the function closing syntax.

The it callback function is closed with a parenthesis ) instead of a curly brace }. This causes a syntax error. Replacing it with } fixes the block closure.

🚀 Application

expert

How many tests run with this Hardhat test file?

Given this test file, how many individual tests will run when executing npx hardhat test?

Blockchain / Solidity

describe('ContractA', function () {
  it('test 1', async function () {});
  it('test 2', async function () {});

  describe('Nested Suite', function () {
    it('test 3', async function () {});
  });
});

describe('ContractB', function () {
  it('test 4', async function () {});
});

A 3

B 4

C 2

D 5

💡 Hint

Count all it blocks, including nested ones.

There are 4 it blocks total: two in ContractA top level, one nested inside Nested Suite, and one in ContractB.