How to use the rxjs-marbles/jasmine/angular.fakeSchedulers function in rxjs-marbles

describe("fakeSchedulers", () => {
  it(
    "should support a timer",
    fakeSchedulers(() => {
      let received: number | undefined;
      timer(100).subscribe(value => (received = value));
      tick(50);
      expect(received).not.toBeDefined();
      tick(50);
      expect(received).toBe(0);
    })
  );

  it(
    "should support delay",
    fakeSchedulers(() => {
      let received: number | undefined;
      of(1)
        .pipe(delay(100))
        .subscribe(value => (received = value));