How to mock Pipe when testing Component

Question

Currently I am overriding providers to use mocked services like this:

beforeEach(inject([TestComponentBuilder], (tcb: TestComponentBuilder) => {
    tcb.overrideProviders(AddFieldToObjectDropdownComponent,
        [
             provide(ServiceA, { useClass: MockServiceA })),
             provide(ServiceB, { useClass: MockServiceB }))
        ])...

I want to do same thing for pipes that the component uses. I tried, provide(PipeA, { useClass: MockPipeA }) and provide(PipeA, { useValue: new MockPipeA() }) but both didn't work.

Answer 1

You can add your mockpipes in the declarations of the TestBed:

TestBed.configureTestingModule({
            declarations: [
                AppComponent,
                MockPipe
            ],
           ...

The MockPipe needs to have the @Pipe decorator with the original name.

import {Pipe, PipeTransform} from '@angular/core';

@Pipe({name: 'pipename'})
class MockPipe implements PipeTransform {
    transform(value: number): number {
        //Do stuff here, if you want
        return value;
    }
}

Answer 2

To stub the pipe, use Dinistro's answer. To spy on the pipe, you can complement that with the following:

let pipeSpy: jasmine.Spy;

beforeEach(() => {
    TestBed.configureTestingModule...

    pipeSpy = spyOn(MockPipe.prototype, 'transform');
};

it('should do whatever', () => {
    doYourStuff();

    expect(pipeSpy).toHaveBeenCalled();
}

Answer 3

Mocking my pipe into simple class like

export class DateFormatPipeMock {
 transform() {
  return '29.06.2018 15:12';
 }
}

and simple use of useClass in my spec file

{provide: DateFormatPipe, useClass: DateFormatPipeMock}

worked for me :-)