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How to test a routing resolver in Angular application

If you did not read "How to test a route", please do it first.

When we want to test a resolver it means we need to mock everything except the resolver and RouterModule. Optionally, we can disable guards to avoid influence of their mocked methods returning falsy values and blocking routes.

beforeEach(() =>  MockBuilder(DataResolver, TargetModule)    .exclude(NG_MOCKS_GUARDS)    .keep(RouterModule)    .keep(RouterTestingModule.withRoutes([])));

To test the resolver we need to render RouterOutlet.

const fixture = MockRender(RouterOutlet);

Additionally, we also need to properly customize mocked services if the resolver is using them to fetch data.

const dataService = TestBed.get(DataService); = () => from([false]);

The next step is to go to the route where the resolver is, and to trigger initialization of the router.

const location = TestBed.get(Location);const router = TestBed.get(Router);
location.go('/target');if (fixture.ngZone) { => router.initialNavigation());  tick();}

Because data is provided to a particular route, we need to find its component in the fixture and to extract ActivatedRoute from its injector. Let's pretend that /target renders TargetComponent.

const el = ngMocks.find(fixture, TargetComponent);const route: ActivatedRoute = el.injector.get(ActivatedRoute);

Profit, now we can assert the data the resolver has provided.

expect({  data: {    flag: false,  },});

Live example#
import { Location } from '@angular/common';import { Component, Injectable, NgModule } from '@angular/core';import { fakeAsync, TestBed, tick } from '@angular/core/testing';import {  ActivatedRoute,  Resolve,  Router,  RouterModule,  RouterOutlet,} from '@angular/router';import { RouterTestingModule } from '@angular/router/testing';import { MockBuilder, MockRender, ngMocks } from 'ng-mocks';import { combineLatest, from, Observable, of } from 'rxjs';import { map } from 'rxjs/operators';
// A simple service simulating a data request.@Injectable()class DataService {  protected flag = true;
  public data(): Observable<boolean> {    return from([this.flag]);  }}
// A resolver we want to test.@Injectable()class DataResolver implements Resolve<{ flag: boolean }> {  public constructor(protected service: DataService) {}
  public resolve() {    return combineLatest([]).pipe(      map(([flag]) => ({ flag })),    );  }}
// A resolver we want to ignore.@Injectable()class MockResolver implements Resolve<{ mock: boolean }> {  protected mock = true;
  public resolve() {    return of({ mock: this.mock });  }}
// A dummy component.// It will be replaced with a mock copy.@Component({  selector: 'target',  template: 'target',})class TargetComponent {}
// Definition of the routing module.@NgModule({  declarations: [TargetComponent],  exports: [RouterModule],  imports: [    RouterModule.forRoot([      {        component: TargetComponent,        path: 'target',        resolve: {          data: DataResolver,          mock: MockResolver,        },      },    ]),  ],  providers: [DataService, DataResolver, MockResolver],})class TargetModule {}
describe('TestRoutingResolver', () => {  // Because we want to test the resolver, it means that we want to  // test its integration with RouterModule. Therefore, we pass  // the resolver as the first parameter of MockBuilder. Then, to  // correctly satisfy its initialization, we need to pass its module  // as the second parameter. And, the last but not the least, we  // need to keep RouterModule to have its routes, and to  // add RouterTestingModule.withRoutes([]), yes yes, with empty  // routes to have tools for testing.  beforeEach(() => {    return MockBuilder(DataResolver, TargetModule)      .keep(RouterModule)      .keep(RouterTestingModule.withRoutes([]));  });
  // It is important to run routing tests in fakeAsync.  it('provides data to on the route', fakeAsync(() => {    const fixture = MockRender(RouterOutlet);    const router: Router = TestBed.get(Router);    const location: Location = TestBed.get(Location);    const dataService: DataService = TestBed.get(DataService);
    // DataService has been replaced with a mock copy,    // let's set a custom value we will assert later on. = () => from([false]);
    // Let's switch to the route with the resolver.    location.go('/target');
    // Now we can initialize navigation.    if (fixture.ngZone) { => router.initialNavigation());      tick(); // is needed for rendering of the current route.    }
    // Checking that we are on the right page.    expect(location.path()).toEqual('/target');
    // Let's extract ActivatedRoute of the current component.    const el = ngMocks.find(TargetComponent);    const route: ActivatedRoute = el.injector.get(ActivatedRoute);
    // Now we can assert that it has expected data.    expect(      jasmine.objectContaining({        data: {          flag: false,        },      }),    );  }));});