fails:Integer#downto [stop] when self and stop are Fixnums does not yield when stop is greater than self
fails:Integer#downto [stop] when self and stop are Fixnums yields once when stop equals self
fails:Integer#downto [stop] when self and stop are Fixnums yields while decreasing self until it is less than stop
fails:Integer#downto [stop] when self and stop are Fixnums yields while decreasing self until it less than ceil for a Float endpoint
fails:Integer#downto [stop] when self and stop are Fixnums raises an ArgumentError for invalid endpoints
fails:Integer#downto [stop] when self and stop are Fixnums returns an Enumerator
