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.

Solution 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;
    }
}

Solution 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();
}

Solution 3

If you want reusable util function for mocking pipes, you can try this option:

export function mockPipe(options: Pipe): Pipe {
    const metadata: Pipe = {
      name: options.name
    };

    return <any>Pipe(metadata)(class MockPipe {});
}

And then just call this function inside the TestBed declarations array:

TestBed.configureTestingModule({
    declarations: [
        SomeComponent,
        mockPipe({ name: 'myPipe' }),
        mockPipe({ name: 'myOtherPipe' })
    ],
    // ...
}).compileComponents();

Solution 4

One possibility is to use the ng-mocks library and use it like this:

TestBed.configureTestingModule({
  declarations: [
    TestedComponent,
    MockPipe(ActualPipe, (...args) => args[0]),
  ]
}).compileComponents();

The second argument to MockPipe defines what the transform function returns for an array of args.

Solution 5

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

providers: [
  ...
  {provide: DateFormatPipe, useClass: DateFormatPipeMock}
  ...
]

worked for me :-)

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