21. Test an effect

In this section we will use marble tests to test our effects observable streams.

1. Fix broken EventComponent test

• Add the dispatch method to our fake Store provided.

src/app/event/containers/event/event.component.spec.ts

import { async, ComponentFixture, TestBed } from '@angular/core/testing';

import { EventComponent } from './event.component';
import { NO_ERRORS_SCHEMA } from '@angular/core';
import { EventService } from '../../services/event.service';
import { Store } from '@ngrx/store';

describe('EventComponent', () => {
  let component: EventComponent;
  let fixture: ComponentFixture<EventComponent>;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      providers: [
        {
          provide: EventService,
          useValue: {
            getAttendees: () => {},
          }
        },
        {
          provide: Store,
          useValue: {
            pipe: () => {},
            dispatch: () => {}
          }
        }
      ],
      declarations: [EventComponent],
      schemas: [NO_ERRORS_SCHEMA]
    }).compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(EventComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

2. Install jest-marbles

Important to use @latest which is for version 6 of RxJS.

• More docs https://github.com/ReactiveX/rxjs/blob/master/doc/writing-marble-tests.md.

npm i jest-marbles@latest -D

3. Add effect spec file

• Add attendees.effects.spec.ts file.

Unknown why toBeObservable Matcher not working with jest?

src/app/event/state/attendees/attendees.effects.spec.ts

import { TestBed } from '@angular/core/testing';
import { provideMockActions } from '@ngrx/effects/testing';
import { hot, cold } from 'jest-marbles';
import { of, Observable } from 'rxjs';

import { AttendeesEffects } from './attendees.effects';
import {
  LoadAttendees,
  LoadAttendeesSuccess,
  AttendeesActions
} from './attendees.actions';
import { Attendee } from '../../../models';
import { EventService } from '../../services/event.service';

describe(`Effect: Attendess`, () => {
  let actions: Observable<AttendeesActions>;
  let effects: AttendeesEffects;
  let service: EventService;

  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [],
      providers: [
        AttendeesEffects,
        provideMockActions(() => actions),
        {
          provide: EventService,
          useValue: {
            getAttendees: jest.fn()
          }
        }
      ]
    });

    service = TestBed.get(EventService);
    effects = TestBed.get(AttendeesEffects);
  });

  it('should return a cold Observable of LoadAttendeesSuccess action', () => {
    const fakeAttendees = [
      { name: 'Duncan', attending: false, guests: 0 } as Attendee
    ];
    const action = new LoadAttendees();
    const completion = new LoadAttendeesSuccess(fakeAttendees);

    jest
      .spyOn(service, 'getAttendees')
      .mockImplementation(() => of(fakeAttendees));

    actions = hot('--a-', { a: action });
    const expected = cold('--(b)', { b: completion });
    expect(effects.getAttendees$).toBeObservable(expected);
  });
});

StackBlitz Link

Duncanhunter - Angular And Ngrx Demo App - StackBlitzStackBlitz

Web Link: Link to the demo app running in StackBlitz

Extras and Homework

These extra sections are for doing after the course or if you finish a section early. Please move onto the next section if doing this as a workshop when the instructor advises.

WARNING: Some of these extra sections will make it more difficult to copy and paste the code examples later on in the course.

You might need to apply the code snippet examples a little more carefully amongst any "extras section" code you may add. If you are up for some extra challenges these sections are for you.

Read more about testing observables

Testing Observables in AngularMedium