How to mock a service in acceptance test in Loopback 4

Question

I am writing some tests in Loopback 4 and I need to mock / stub a service, I mean I need to replace it in bindings by a stub one. But I can't find how to do this.

I want to write tests such as this one :

it(`should work if a user was found for the token in 'authorization' header`, async () => {
  await client
    .get('/mock')
    .set('Authorization', 'Bearer a-good-token')
    .expect(200);
});

For this I have to start an application before each test suite in before method. I boot my application then I try to change the binding for my service :

before('setupApplication', async () => {
  app = new MyApplication();
  await app.boot();
  app.bind('services.WebAuthService').to(MockWebAuthService); // to replace with the mocked one
  app.controller(MockController);
  await app.start();
}

I tried different ways to write my MockWebAuthService :

• With Sinon stub :

const utilisateur = sinon.createStubInstance(Utilisateur);
utilisateur.uId = 123456;
const verifyCredentialsStub = sinon.stub().resolves(undefined);
verifyCredentialsStub
  .withArgs({token: 'a-good-token'})
  .resolves(utilisateur);
const MockWebAuthService: WebAuthService = sinon.createStubInstance(
  WebAuthService,
  {
    verifyCredentials: verifyCredentialsStub,
    convertToUserProfile: sinon.stub(),
  },
);

• Or with a new class :

class MockWebAuthService implements UserService<Utilisateur, Credentials> {

  async verifyCredentials(credentials: Credentials): Promise<Utilisateur> {
    const utilisateur = sinon.createStubInstance(Utilisateur);
    utilisateur.uId = 123456;
    if (credentials.token === 'a-good-token') {
      return utilisateur;
    } else {
      throw new Error('invalid token');
    }
  }

  convertToUserProfile(utilisateur: Utilisateur): UserProfile {
    return {} as UserProfile;
  }
}

But none of these works. The WebAuthService that is injected in my components is still the one from src/services, not the mocked one.

Any idea how I should do that ?

Thanks in advance for your help !

Answer 1

I found my problem. I was wrong in the way I binded the stub service.

It works this way :

app.getBinding('services.WebAuthService').to(MockWebAuthService);