fails:Rational#+ calls #coerce on the passed argument with self
fails:Rational#+ calls #+ on the coerced Rational with the coerced Object
fails:Rational#+ with a Rational returns the result of substracting other from self as a Rational
fails:Rational#+ with a Float returns the result of substracting other from self as a Float
fails:Rational#+ with an Integer returns the result of substracting other from self as a Rational
