fails:Float#phase returns NaN if NaN
fails:Float#phase returns self if NaN
fails:Float#phase returns 0 if positive
fails:Float#phase returns 0 if +0.0
fails:Float#phase returns 0 if +Infinity
fails:Float#phase returns Pi if negative
fails:Float#phase returns Pi if -0.0
fails:Float#phase returns Pi if -Infinity
