Test pipe with dependencies on services

Because of the DI in your pipe, you need to configure a test environment (test bed) to resolve the dependency:

import { BrowserModule, DomSanitizer } from '@angular/platform-browser';import { inject, TestBed } from '@angular/core/testing';describe('SanitiseHtmlPipe', () => {  beforeEach(() => {    TestBed      .configureTestingModule({        imports: [          BrowserModule        ]      });  });  it('create an instance', inject([DomSanitizer], (domSanitizer: DomSanitizer) => {    let pipe = new SanitiseHtmlPipe(domSanitizer);    expect(pipe).toBeTruthy();  })); });

just in case anyone would like to reuse the constructor of the Pipe, you can use the TestBed to acheive the same result :

  let pipe: SafeHtmlPipe;  let sanitized: DomSanitizer  beforeEach(async() => {    TestBed.configureTestingModule({      providers: [DomSanitizer]    });    sanitized = TestBed.get(DomSanitizer);    pipe = new SafeHtmlPipe(sanitized);  });  it('create an instance', () => {    expect(pipe).toBeTruthy();  });

In case you want to mock the whole providers and don't wanna use the constructor, this is how I do it (with Jest but replace the spy with your regular jasmine.createSpyObj)

spec

describe("MyPipe", () => {  let pipe: MyPipe;  const myServiceSpy = { myFunction: jest.fn() };  beforeEach(() => {    jest.clearAllMocks();    TestBed.configureTestingModule({      providers: [        MyPipe,        {          provide: MyService,          useValue: myServiceSpy        }      ]    });    pipe = TestBed.inject(myPipe);  });  it("create an instance", () => {    expect(pipe).toBeTruthy();  });});

pipe

@Pipe({  name: "myPipe"})export class MyPipe implements PipeTransform {  constructor(private readonly myService: MyService) {}  transform(value: Item): boolean {    // stuff with your service    return true;  }}