Testing

Projects created with nest new come with Jest, Supertest and Nest's testing package, @nestjs/testing, already configured. This chapter covers unit tests for services and controllers, end-to-end tests that boot the whole application, and testing a plain Express app with Supertest.

Running tests

Unit tests are the *.spec.ts files inside src; end-to-end tests are the *.e2e-spec.ts files in test, which use their own Jest config, test/jest-e2e.json.

npm run test         # unit tests
npm run test:watch   # re-run on file changes
npm run test:cov     # coverage report
npm run test:e2e     # end-to-end tests

Unit testing a service

A service without dependencies can be tested like any class, by calling new. When it has dependencies, build a testing module with Test.createTestingModule and replace real providers with fakes.

// src/users/users.service.spec.ts
import { Test } from "@nestjs/testing";
import { getRepositoryToken } from "@nestjs/typeorm";
import { User } from "./entities/user.entity";
import { UsersService } from "./users.service";

describe("UsersService", () => {
  let service: UsersService;
  const repository = { find: jest.fn(), create: jest.fn(), save: jest.fn() };

  beforeEach(async () => {
    const moduleRef = await Test.createTestingModule({
      providers: [UsersService, { provide: getRepositoryToken(User), useValue: repository }],
    }).compile();

    service = moduleRef.get(UsersService);
  });

  it("returns every user", async () => {
    repository.find.mockResolvedValue([{ id: 1, name: "Kim" }]);
    await expect(service.findAll()).resolves.toHaveLength(1);
  });
});

getRepositoryToken(User) is the injection token that @InjectRepository(User) looks up, so the service logic runs without a database.

Unit testing a controller

For controllers, fake the service. When you register the real provider and want to swap it, use overrideProvider.

// src/users/users.controller.spec.ts
import { Test } from "@nestjs/testing";
import { UsersController } from "./users.controller";
import { UsersService } from "./users.service";

describe("UsersController", () => {
  it("delegates to the service", async () => {
    const usersService = { findAll: jest.fn().mockResolvedValue([]) };

    const moduleRef = await Test.createTestingModule({
      controllers: [UsersController],
      providers: [UsersService],
    })
      .overrideProvider(UsersService)
      .useValue(usersService)
      .compile();

    const controller = moduleRef.get(UsersController);
    await controller.findAll();
    expect(usersService.findAll).toHaveBeenCalled();
  });
});

End-to-end tests with Supertest