Error in Angular unit testing: Service property is not utilizing the value set by spyOnProperty

I am currently working on creating a negative test scenario for my AuthService. The specific test case involves verifying that a property in the constructor is set to null if the angularFireAuth does not return any data. While the positive test case is functioning as expected, I am encountering some challenges with setting up the negative test scenario. Even with the spyOnProperty mock implementation, I am observing that the property is returning null when I subscribe to it.

The issue seems to be related to getting the service constructor to recognize the mocked null value from the spyOnProperty. In the case of a component, I would typically use fixture.detectChanges, but this approach does not work for a service. Is there a specific method or technique that I should be using to properly rebuild the service so that the constructor can pick up the mocked null value?

AuthService Constructor

{
(this.partyCollectionPath);
    this.afAuth.authState.subscribe((user: User | null) => {
      if (user) {
        this.userData = {
          uid: user.uid,
          email: user.email,
          emailVerified: user.emailVerified
        };
        this.liveUid = user.uid
      } else {
        this.userData = null
      }
    });
  }

AngularFireAuthMock

import { User } from '../shared/interface/user';
import { of } from 'rxjs';

const authState: User = {
    uid: 'fakeuser',
    email: '<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="2a5e4f595e6a5e4f595e04494547">[email protected]</a>',
    emailVerified: true
};
export const AngularFireAuthMock: any = {
    AngularFireAuth: jasmine.createSpyObj('AngularFireAuth', {
//other functions
}),

get authState() {
    return of(authState);
  },

Test Assertion

  it('userData set to null', () => {

    const spy = spyOnProperty(AngularFireAuthMock, 'authState', 'get');
    spy.and.returnValue(of(null))

    AngularFireAuthMock.authState.subscribe((data: any) => {
      
      console.log('subscribe: ', data)
      
    })
    console.log('userData: ', service.userData) 
    // expect(service.userData).toBeNull()

  });

Console Logs

LOG: 'subscribe: ', null

LOG: 'userData: ', Object{uid: 'fakeuser', email: '[email protected]', emailVerified: true}

Answer №1

When working with asynchronous code in the subscribe method, it's important to remember that the code below the subscribe is executed synchronously and may not wait for the asynchronous call to complete. To ensure that the test waits for the asynchronous API call to finish, you can utilize the fakeAsync and flush functions.

If the console.log statement runs before the subscribe method completes, it can lead to issues and unexpected behavior.

it('userData set to null', fakeAsync(() => {
    const spy = spyOnProperty(AngularFireAuthMock, 'authState', 'get');
    spy.and.returnValue(of(null));
    AngularFireAuthMock.authState.subscribe((data: any) => {
      console.log('subscribe: ', data);
    })
    flush();
    console.log('userData: ', service.userData) 
    // expect(service.userData).toBeNull()

}));

Answer №2

My struggle with understanding the basic structure of TestBed in Angular tests led me to dive into the documentation on testing services. It became clear to me that TestBed.inject() is the command used to build the service for testing purposes.

Typically, in the auto-generated .spec file for a service, TestBed.inject() is placed inside the beforeEach(). This caused an issue where the constructor was being constructed before my spyOnProperty was executed. The solution was to move TestBed.inject() outside of the beforeEach() block and run it after my spy.

Below is the finalized solution:

AuthService

 // Code for AuthService to test

AngularFireAuthMock

 // Code for AngularFireAuthMock

auth.service.spec.ts

There were multiple ways to approach this, and the documentation did not favor one over the other. Initially, I chose to remove TestBed.inject() from the beforeEach() and manually include it in each test. However, to streamline the process and avoid manual injection, I created two describe blocks with different beforeEach() setups. This way, I could easily switch between different mock files using the provide useValue instead of spyOnProperty. If there is a standard or better practice for this, I am open to suggestions!

 // Code for AuthService testing with different beforeEach setups

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