Test lifecycle hooks (before, after) in Node.js - Mini Project: Build & Apply

Test lifecycle hooks (before, after) in Node.js

📖 Scenario: You are writing tests for a simple calculator module in Node.js. You want to prepare some setup before tests run and clean up after all tests finish.

🎯 Goal: Build a test file using before and after hooks to initialize and reset a variable around your tests.

📋 What You'll Learn

Create a variable counter initialized to 0

Use a before hook to set counter to 5 before tests

Write a test that checks counter equals 5

Use an after hook to reset counter to 0 after tests

💡 Why This Matters

🌍 Real World

Test lifecycle hooks help prepare and clean up resources like database connections or test data before and after tests run.

💼 Career

Understanding test hooks is essential for writing reliable automated tests in Node.js projects, a common skill in software development jobs.

1

DATA SETUP: Create a variable counter initialized to 0

Create a variable called counter and set it to 0.

Node.js

// Create a variable called counter and set it to 0
// Your code here

Hint

Use let counter = 0; to create the variable.

2

CONFIGURATION: Add a before hook to set counter to 5

Add a before hook that sets counter to 5 before tests run.

Node.js

let counter = 0;

// Add a before hook to set counter to 5
// Your code here

Hint

Use before(() => { counter = 5; }); to set up before tests.

3

CORE LOGIC: Write a test that checks counter equals 5

Write a test using it named 'counter should be 5' that asserts counter === 5 using strictEqual from assert.

Node.js

let counter = 0;

before(() => {
    counter = 5;
});

// Write a test named 'counter should be 5' that checks counter === 5
// Your code here

Hint

Use it('counter should be 5', () => { assert.strictEqual(counter, 5); }); to write the test.

4

COMPLETION: Add an after hook to reset counter to 0

Add an after hook that resets counter to 0 after all tests run.

Node.js

import assert from 'assert';

let counter = 0;

before(() => {
    counter = 5;
});

it('counter should be 5', () => {
    assert.strictEqual(counter, 5);
});

// Add an after hook to reset counter to 0
// Your code here

Hint

Use after(() => { counter = 0; }); to clean up after tests.

Practice

1. What is the main purpose of the before hook in Node.js testing frameworks like Mocha?

easy

A. To run setup code once before all tests in a suite

B. To run cleanup code after each test

C. To run code before each individual test

D. To skip a test conditionally

Solution

1. Step 1: Understand the role of before hook

   The before hook runs once before all tests in a test suite to prepare the environment.

2. Step 2: Differentiate from other hooks

   beforeEach runs before each test, and after runs after all tests, so they do not match the question.

3. Final Answer:

   To run setup code once before all tests in a suite -> Option A

4. Quick Check:

   before = setup once before all tests [OK]

Hint: Remember: before = once before all tests [OK]

Common Mistakes:

• Confusing before with beforeEach
• Thinking before runs after tests
• Mixing before with afterEach

2. Which of the following is the correct syntax to define a beforeEach hook in Mocha?

easy

A. before_each(() => { /* setup code */ });

B. beforeEach(() => { /* setup code */ });

C. beforeEach {}

D. beforeEach: function() { /* setup code */ }

Solution

1. Step 1: Recall Mocha hook syntax

   Mocha uses functions like beforeEach(() => { ... }) to define hooks.

2. Step 2: Check each option

   beforeEach(() => { /* setup code */ }); uses correct arrow function syntax. before_each(() => { /* setup code */ }); uses invalid function name. beforeEach {} is incomplete syntax. beforeEach: function() { /* setup code */ } uses incorrect object notation.

3. Final Answer:

   beforeEach(() => { /* setup code */ }); -> Option B

4. Quick Check:

   Correct hook syntax uses function call with callback [OK]

Hint: Use camelCase and parentheses for hooks [OK]

Common Mistakes:

• Using underscores instead of camelCase
• Omitting parentheses
• Using object notation instead of function call

3. Consider this Mocha test code snippet:

let count = 0;
before(() => { count += 1; });
after(() => { count += 10; });
it('test 1', () => { count += 100; });
it('test 2', () => { count += 1000; });

What is the final value of count after all tests run?

medium

A. 1110

B. 1112

C. 111

D. 1111

Solution

1. Step 1: Calculate increments in order

   before runs once: count = 0 + 1 = 1.
   Then test 1: count = 1 + 100 = 101.
   Then test 2: count = 101 + 1000 = 1101.
   Finally after: count = 1101 + 10 = 1111.

2. Step 2: Confirm no other increments

   No beforeEach or afterEach hooks affect count, so final is 1111.

3. Final Answer:

   1111 -> Option D

4. Quick Check:

   Sum increments: 1 + 100 + 1000 + 10 = 1111 [OK]

Hint: Add increments in hook and test order [OK]

Common Mistakes:

• Adding after hook before tests
• Forgetting before hook runs once
• Confusing beforeEach with before

4. Given this Mocha test code:

before(() => { console.log('Setup'); });
after(() => { console.log('Cleanup'); });

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

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

What is the correct order of console output?

medium

A. Test 1, Test 2, Setup, Cleanup

B. Test 1, Setup, Test 2, Cleanup

C. Setup, Test 1, Test 2, Cleanup

D. Setup, Test 1, Cleanup, Test 2

Solution

1. Step 1: Understand hook execution order

   before runs once before all tests, so 'Setup' prints first.

2. Step 2: Tests run in order, then after hook

   Tests print 'Test 1' then 'Test 2'. After all tests, after runs printing 'Cleanup'.

3. Final Answer:

   Setup, Test 1, Test 2, Cleanup -> Option C

4. Quick Check:

   before -> tests -> after = Setup, Test 1, Test 2, Cleanup [OK]

Hint: before runs once first; after runs once last [OK]

Common Mistakes:

• Assuming after runs after each test
• Mixing test order
• Thinking before runs before each test

5. You want to open a database connection once before all tests and close it once after all tests. Which hook pair should you use in Mocha?

hard

A. before to open and after to close

B. beforeEach to open and afterEach to close

C. after to open and before to close

D. beforeEach to open and after to close

Solution

1. Step 1: Identify when to open connection

   Opening once before all tests means using before hook.

2. Step 2: Identify when to close connection

   Closing once after all tests means using after hook.

3. Final Answer:

   before to open and after to close -> Option A

4. Quick Check:

   Open once before all, close once after all [OK]

Hint: Use before/after for once-only setup/cleanup [OK]

Common Mistakes:

• Using beforeEach/afterEach causing repeated open/close
• Reversing before and after roles
• Mixing hooks for different purposes