Angular testing how to prevent ngOnInit call to test a method directly

Question

Context

I have a component. Inside of it, the ngOnInit function calls another function of component to retrieve user List. I want to make two series of tets:

Answer 1

it(`should get the user List via refresh function`, fakeAsync(() => {
  let ngOnInitFn = UserListComponent.prototype.ngOnInit;
  UserListComponent.prototype.ngOnInit = () => {} // override ngOnInit
  comp.onRefreshUserList();
  tick();

  fixture.detectChanges(); 
  UserListComponent.prototype.ngOnInit = ngOnInitFn; // revert ngOnInit

  expect(comp.userList.length).toBe(3, 'user list after function call');
}));

Plunker Example