fails:Integer#downto [stop] when self and stop are Fixnums when no block is given returned Enumerator size raises an ArgumentError for invalid endpoints
fails:Integer#downto [stop] when self and stop are Fixnums when no block is given returned Enumerator size returns self - stop + 1
fails:Integer#downto [stop] when self and stop are Fixnums when no block is given returned Enumerator size returns 0 when stop > self
