Unit testing controllers in NestJS - Mini Project: Build & Apply

Unit Testing Controllers in NestJS

📖 Scenario: You are building a simple NestJS application that manages books. You want to make sure your controller works correctly by writing unit tests for it.

🎯 Goal: Create a unit test for a NestJS controller called BooksController that has a method findAll returning a list of books.

📋 What You'll Learn

Create a BooksController class with a findAll method returning an array of book objects

Create a unit test file for BooksController

Set up a testing module with BooksController in the test

Write a test case that checks findAll returns the expected books array

💡 Why This Matters

🌍 Real World

Unit testing controllers ensures your API endpoints behave as expected before deploying your NestJS application.

💼 Career

Writing unit tests for controllers is a key skill for backend developers working with NestJS to maintain reliable and maintainable code.

1

Create the BooksController with findAll method

Create a class called BooksController with a method findAll that returns this exact array: [{ id: 1, title: '1984' }, { id: 2, title: 'Brave New World' }].

NestJS

# Your code here

Need a hint?

Define a class with a method that returns the exact array of book objects.

2

Set up the testing module with BooksController

In a test file, import Test and TestingModule from @nestjs/testing. Create a variable booksController. Use beforeEach to create a testing module with BooksController as a controller and assign the controller instance to booksController.

NestJS

export class BooksController {
  findAll() {
    return [
      { id: 1, title: '1984' },
      { id: 2, title: 'Brave New World' }
    ];
  }
}

// Your test setup here

Need a hint?

Use NestJS testing utilities to create a module and get the controller instance.

3

Write a test case for findAll method

Inside the describe block, add a test case with it named 'should return an array of books'. Inside it, call booksController.findAll() and expect the result to equal the exact array [{ id: 1, title: '1984' }, { id: 2, title: 'Brave New World' }].

NestJS

import { Test, TestingModule } from '@nestjs/testing';

export class BooksController {
  findAll() {
    return [
      { id: 1, title: '1984' },
      { id: 2, title: 'Brave New World' }
    ];
  }
}

describe('BooksController', () => {
  let booksController: BooksController;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      controllers: [BooksController],
    }).compile();

    booksController = module.get(BooksController);
  });

  // Add your test case below
  
  // Your code here
});

Need a hint?

Write a test that calls findAll and checks the returned array matches exactly.

4

Complete the test file with proper imports and structure

Add the import statement for describe, it, and expect from @jest/globals at the top. Ensure the test file exports nothing and contains the full test suite for BooksController with the test case for findAll.

NestJS

// Add import for describe, it, expect from '@jest/globals'

import { Test, TestingModule } from '@nestjs/testing';

export class BooksController {
  findAll() {
    return [
      { id: 1, title: '1984' },
      { id: 2, title: 'Brave New World' }
    ];
  }
}

// Your test suite below

Need a hint?

Jest globals like describe, it, and expect should be imported explicitly.