Mocking a return value for a Subject - Unit Testing with Jasmine

Question

I'm unit testing and part of the testing has a Subject. I'm new to Subjects and get the general gist of how they work but am struggling to mock a return value on one. I've tried various ways in the hopes of stumbling on the correct way like using a spy and returnvalue to return the number 3.

In the component:

.... 
private searchEvent: Subject<string> = new Subject<string>();

....
      this.searchEvent.pipe(debounceTime(500)).subscribe(value => {
        if (value.length >= 3) {
          this.retrieveAssets(value);
        }
      })
....

In my spec file I basically have:

        component['searchStockEvent'].subscribe(x=> of(3));

        fixture.whenStable().then(() => {
          expect(component['retrieveAssets']).toHaveBeenCalled();
        });

Answer 1

searchEvent being private will make it difficult to call next directly on the subject so you have to find a way of what makes searchEvent emit a value of greater than 3 and go that route.

For this demo, we will make it public:

.... 
public searchEvent: Subject<string> = new Subject<string>();

....
      this.searchEvent.pipe(debounceTime(500)).subscribe(value => {
        if (value.length >= 3) {
          this.retrieveAssets(value);
        }
      })
....

import { fakeAsync, tick } from '@angular/core/testing';
it('should call retrieve assets', fakeAsync(() => {
  component.searchEvent.next(3);
  // we need to pass 501ms in a fake way
  tick(501);
  expect(component.retreiveAssets).toHaveBeenCalled();
}));