How to create unit test of virtualScroll in table prime Ng

Question

I can't test virtualScroll with lazayload in table

  <p-table class="basicTable" [value]="cars" [scrollable]="true" [rows]="100" scrollHeight="500px"
             (onLazyLoad)="load($event)" [rows]="100" lazy="true"
             [virtualScroll]="true">

  const tableEl = fixture.debugElement.query(By.css('.p-datatable-virtual-scrollable-body'));
    fixture.detectChanges();
    const bodyRows = tableEl.query(By.css('.p-datatable-tbody')).queryAll(By.css('tr'));
    console.log(bodyRows)

bodyRows is empty

thanks

Answer 1

The Angular teams unit tests provided me an answer to this. There's a number of async steps before the CDK Virtual Scroll displays data, so we have to simulate these. Instead of fixture.detectChanges() , add the following function to the top of your .spec.ts file and call it while passing the fixture as a param:

const finishInit = (fixture: ComponentFixture<any>) => {
  // On the first cycle we render and measure the viewport.
  fixture.detectChanges();
  flush();

  // On the second cycle we render the items.
  fixture.detectChanges();
  flush();

  // Flush the initial fake scroll event.
  tick(500);
  flush();
  fixture.detectChanges();
};

Your it will also need to use fakeAsync

it('should display virtual scroll data', fakeAsync(() => {


}));