Unit Test for function with mat paginator method firstPage()

Question

I have a function I am trying to test. I am using the matPaginator.firstPage() method inside of it. However any test I write for this function I can an error of

"Cannot read property 'firstPage' of undefined"

I cannot find anything on how to mock paginator in unit tests or provided it in my spec file that will allow this test to complete.

Any help/suggestions/tips would be much appreciated.

Answer 1

it('area of business selected should be in active Filter Chip Object', () => {
 component.selectedBusinessArea = 'Fake Business';
 component.activeFilterChips = [];
 component.activeFilterObj = {};
 fixture.detectChanges();
 fixture.whenStable().then(() => {
  spyOn(component.paginator, 'firstPage').and.returnValue('');
  component.startFilter();
  fixture.detectChanges();
  expect(component.activeFilterChips).toBe([{
    option: "businessArea",
    value: "Fake Business"
  }]);
 })
});

Creating a spyOn for the firstPage() for paginator and wrapping that inside of the whenStable() has my test passing. Not sure if that is the correct way of handling it. Also, I am not trying to test the firstPage() so I gave a returnValue of ''.