@Test
public void testSumOfAFewDoubles() throws Throwable {

    Observable<Double> src = Observable.from(0.0d, 1.0d, 0.5d);
    sumDoubles(src).subscribe(wd);
    verify(wd, times(1)).onNext(anyDouble());
    verify(wd).onNext(1.5d);
    verify(wd, never()).onError(any(Throwable.class));
    verify(wd, times(1)).onCompleted();
}