Angular testing why is flush necessary when clicking but not in triggerEventHandler

I have an Angular module with a list, card, detail, and edit components.

The list template would look like this:

<own-list>
<button [routerLink]="['/', 'mod', 'create']" data-testid="new-request">Create</button>
<own-card *ngFor="let elem of elements" [routerLink]="['/', 'mod', elem.id]"></own-card>
<own-list>


When testing that when clicking the card it goes to its detail page:

test('it should navigate to detail when clicking a card', fakeAsync(() => {
const cardElems = rootFixture.debugElement.queryAll(By.css('own-card'));
// Navigate to top card detail
cardElems[0].nativeElement.click();
tick();
fixture.detectChanges();
// Check route is correct
expect(location.path()).toBe(`/mod/${sortedElements[0].id}`);
}));


works fine.

When testing that when clicking the create button goes to edit:

test('it should navigate to edit when clicking new request', fakeAsync(() => {
const debugCreateBtn = rootFixture.debugElement.query(By.css(`[data-testid="new-request"]`));
// Navigate to edit
debugCreateBtn.nativeElement.click();
tick();
fixture.detectChanges();
// Check route is correct
expect(location.path()).toBe(`/mod/create`);
}));


it fails with 1 periodic timer(s) still in the queue.

If I add flush as such:

test('it should navigate to edit when clicking new request', fakeAsync(() => {
const debugCreateBtn = rootFixture.debugElement.query(By.css(`[data-testid="new-request"]`));
// Navigate to edit
debugCreateBtn.nativeElement.click();
tick();
fixture.detectChanges();
flush(); // <-- new flush
// Check route is correct
expect(location.path()).toBe(`/mod/create`);
}));


it works well.

And if I switch to triggerEventHandler:

test('it should navigate to edit when clicking new request', fakeAsync(() => {
const debugCreateBtn = rootFixture.debugElement.query(By.css(`[data-testid="new-request"]`));
// Navigate to edit
// Run in ngZone to avoid warning
fixture.ngZone.run(() => debugCreateBtn.triggerEventHandler('click', { button: 0 }));
tick();
fixture.detectChanges();
// Check route is correct
expect(location.path()).toBe(`/mod/create`);
}));


then it works, without the flush.

Could someone explain why it works or doesn't in each situation?

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