What is the process for evaluating an Observable using the subscribe method in an Angular application?

I have a component with the following function:

@Output() data: EventEmitter<any> = new EventEmitter();

testData() {
    observableRef.subscribe(() => {
      this.data.emit();
    }, () => {
      this.data.emit();
    });
  }

I am trying to write unit test cases for this function. Here is what I have tried so far:

it('should call testData method', fakeAsync(() => {
    fixture.detectChanges();
    spyOn(observableRef, 'emit’);
    component.testData(component.data);
    expect(component.data.emit).toHaveBeenCalled();
    tick();
    discardPeriodicTasks();
}));

However, when running this test case, the code coverage does not enter the subscribe function. As a newbie in unit testing, I am unsure why this is happening. Can someone please guide me on how to properly test the subscribe function and improve my test case?

Answer №1

Keep an eye on the observableRef and component.data emissions, then trigger the fixture.detectChanges() method:

import { of } from 'rxjs';

it("should invoke testData function", async(() => {

  spyOn(observableRef, 'emit').and.returnValue(of("some value"))
  spyOn(component.data, 'emit').and.returnValue(of("some value"))
  component.testData();
  fixture.detectChanges();

  expect(component.data.emit).toHaveBeenCalled();
}));

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