@Test
public void testEmptyAverageLongs() throws Throwable {

    Observable<Long> src = Observable.empty();
    averageLongs(src).subscribe(wl);
    verify(wl, never()).onNext(anyLong());
    verify(wl, times(1)).onError(isA(IllegalArgumentException.class));
    verify(wl, never()).onCompleted();
}