Testing Long-Running API Calls#

Let's now test TerrainShopResolver. This resolver should abandon long-running API calls that may prevent a view from being rendered on the server.

TerrainShopResolver doesn't perform HTTP calls; instead, it delegates them to TerrainShopService. This means you don't need to stub the HttpClient service. You can just mock TerrainShopService and return the data from getPromotions() with a specified delay.

Create a new file, src/app/terrain-shop-resolver.service.spec.ts, and add the following import statements:

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

import { TerrainShopResolverService } from './terrain-shop-resolver.service';

import { PLATFORM_ID } from '@angular/core';

import { TerrainShopService } from './terrain-shop.service';

import { Observable } from 'rxjs';

Similar to I18nServiceTests, you want to test service behavior both in the browser and on the server. To do this, you are going to provide a mocked PLATFORM_ID value. Declare a variable that will be used to stub PLATFORM_ID:

let platformId = 'server';

The next step is to prepare a mock of TerrainShopService:

let timeout = 1000;

let terrainServiceMock = {

  getPromotions() {

    return new Observable((observer) => {

      setTimeout(() => {

        observer.next(['testValue']);

        observer.complete();

      }, timeout);

    });

  },

};

The code above introduces the terrainServiceMock variable that holds an object containing the getPromotions() method. This method returns an observable that emits after a timeout defined by the timeout variable. You are going to modify this variable in tests.

When mocks are ready, it's time to write the beforeEach() section, inject a service that you are going to test, and verify that it's instantiated correctly:

describe('Terrain Shop Resolver', () => {

  let service: TerrainShopResolverService;