Integration testing in NestJS - Mini Project: Build & Apply

Integration Testing with NestJS

📖 Scenario: You are building a simple NestJS service that manages a list of books. You want to make sure your service works correctly by writing integration tests that check the full flow of your application.

🎯 Goal: Build a NestJS integration test that sets up the testing module, injects the service, and verifies that the service returns the expected list of books.

📋 What You'll Learn

Create a basic array of book objects as initial data

Set up a NestJS testing module with the service

Write an integration test that calls the service method

Assert the returned data matches the initial book list

💡 Why This Matters

🌍 Real World

Integration tests help ensure that different parts of your NestJS application work together correctly before deploying to users.

💼 Career

Writing integration tests is a key skill for backend developers to maintain reliable and bug-free applications in professional environments.

1

DATA SETUP: Create initial book data

Create a constant array called books with these exact objects: { id: 1, title: 'NestJS Basics' } and { id: 2, title: 'Testing with Jest' }.

NestJS

// Create a constant array called books with two book objects
// Your code here

Need a hint?

Use const books = [ ... ] with two objects inside.

2

CONFIGURATION: Set up NestJS testing module

Create a variable called moduleRef and assign it the result of await Test.createTestingModule({ providers: [BooksService] }).compile() inside an async function.

NestJS

const books = [
  { id: 1, title: 'NestJS Basics' },
  { id: 2, title: 'Testing with Jest' }
];

// Create moduleRef with Test.createTestingModule and compile
// Your code here

Need a hint?

Use await Test.createTestingModule({ providers: [BooksService] }).compile() and assign it to moduleRef.

3

CORE LOGIC: Retrieve service and call method

Create a variable called booksService and assign it the result of moduleRef.get(BooksService). Then call booksService.findAll() and assign the result to result.

NestJS

const books = [
  { id: 1, title: 'NestJS Basics' },
  { id: 2, title: 'Testing with Jest' }
];

const moduleRef = await Test.createTestingModule({
  providers: [BooksService],
}).compile();

// Get booksService from moduleRef and call findAll
// Your code here

Need a hint?

Use moduleRef.get(BooksService) to get the service, then call findAll().

4

COMPLETION: Assert the returned books match initial data

Write an assertion using expect(result).toEqual(books) to check that the service returns the correct book list.

NestJS

const books = [
  { id: 1, title: 'NestJS Basics' },
  { id: 2, title: 'Testing with Jest' }
];

const moduleRef = await Test.createTestingModule({
  providers: [BooksService],
}).compile();

const booksService = moduleRef.get(BooksService);
const result = booksService.findAll();

// Assert that result equals books
// Your code here

Need a hint?

Use expect(result).toEqual(books) to check the returned data.