@Test
public void testEmptySumFloats() throws Throwable {

    Observable<Float> src = Observable.empty();
    sumFloats(src).subscribe(wf);
    verify(wf, times(1)).onNext(anyFloat());
    verify(wf).onNext(0.0f);
    verify(wf, never()).onError(any(Throwable.class));
    verify(wf, times(1)).onCompleted();
}