fails:Integer#gcd returns self if equal to the argument
fails:Integer#gcd returns an Integer
fails:Integer#gcd returns the greatest common divisor of self and argument
fails:Integer#gcd returns a positive integer even if self is negative
fails:Integer#gcd returns a positive integer even if the argument is negative
fails:Integer#gcd returns a positive integer even if both self and argument are negative
fails:Integer#gcd accepts a Bignum argument
fails:Integer#gcd works if self is a Bignum
fails:Integer#gcd raises an ArgumentError if not given an argument
fails:Integer#gcd raises an ArgumentError if given more than one argument
fails:Integer#gcd raises a TypeError unless the argument is an Integer
