
      expect(rx.next).to.have.been.calledTwice;
      expect(rx.next.firstCall).to.have.been.calledWith(2);
      expect(rx.next.secondCall).to.have.been.calledWith(4);
    });

    it('should concatenate the values in the order passed in', () => {
      const input$ = of(1, 2, 3);
      const predicate = (n: number) => of(true).pipe(delay(3 - n));