Test lifecycle hooks (before, after) in Node.js - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the order of console logs with before and after hooks?

Consider this Node.js test code using Mocha framework lifecycle hooks. What will be the order of console output when running this test suite?

Node.js

describe('Suite', () => {
  before(() => console.log('before all'));
  after(() => console.log('after all'));
  beforeEach(() => console.log('before each'));
  afterEach(() => console.log('after each'));

  it('test 1', () => console.log('test 1'));
  it('test 2', () => console.log('test 2'));
});

A before each, before all, test 1, after each, before each, test 2, after each, after all

B before all, before each, test 1, before each, test 2, after each, after each, after all

C before all, before each, test 1, after each, before each, test 2, after each, after all

D before all, test 1, before each, after each, test 2, after each, before each, after all

💡 Hint

Remember that before runs once before all tests, beforeEach runs before each test, and similarly for after and afterEach.

The before hook runs once before all tests. beforeEach runs before each test. afterEach runs after each test. after runs once after all tests.

So the order is: before all, before each, test 1, after each, before each, test 2, after each, after all.

❓ state_output

intermediate

What is the final value of counter after hooks and tests?

Given this test code using Mocha hooks, what is the final value of the variable counter after all tests run?

Node.js

let counter = 0;
describe('Counter Suite', () => {
  before(() => { counter += 1; });
  beforeEach(() => { counter += 2; });
  afterEach(() => { counter += 3; });
  after(() => { counter += 4; });

  it('test 1', () => {});
  it('test 2', () => {});
});

A 15

B 17

C 16

D 18

💡 Hint

Count how many times each hook runs and add their increments carefully.

The before hook runs once: +1

beforeEach runs twice (once per test): 2 * 2 = +4

afterEach runs twice: 2 * 3 = +6

after runs once: +4

Total: 1 + 4 + 6 + 4 = 15

📝 Syntax

advanced

Which option causes a syntax error in Mocha hooks?

Identify which code snippet will cause a syntax error when defining Mocha lifecycle hooks.

A before(() => { console.log('start'); });

B after(function() { console.log('cleanup'); });

C afterEach(() => console.log('done'));

D beforeEach { console.log('setup'); }

💡 Hint

Check the syntax for arrow functions and function calls.

Option D is missing parentheses after beforeEach and uses braces incorrectly. It should be beforeEach(() => { ... }).

All other options use correct syntax.

🔧 Debug

advanced

Why does the after hook not run in this test suite?

Given this Mocha test suite, why does the after hook never execute?

Node.js

describe('My Suite', () => {
  before(() => { throw new Error('fail'); });
  after(() => console.log('after hook'));

  it('test 1', () => {});
});

A Because the after hook is defined after the before hook.

B Because the before hook throws an error, aborting the suite.

C Because the test fails, Mocha stops running hooks.

D Because the test throws an error, the after hook is skipped.

💡 Hint

Consider how Mocha handles failures in before hooks.

When a before hook fails (throws an error), Mocha aborts the entire suite: no tests execute, and after hooks do not run.

after hooks only run after the suite completes (successfully or not), but a failed before prevents suite execution.

🧠 Conceptual

expert

Which hook is best to reset a database connection before each test?

In a Node.js test suite using Mocha, you want to reset the database connection before every test to ensure a clean state. Which lifecycle hook should you use?

A beforeEach()

B before()

C after()

D afterEach()

💡 Hint

Think about how often you want the reset to happen relative to tests.

beforeEach() runs before every test, making it ideal to reset state like database connections before each test.

before() runs once before all tests, so it won't reset between tests.

after() and afterEach() run after tests, not before.