fails:Method#arity returns n, where n is the number of required arguments, when there are zero or more required arguments only
fails:Method#arity returns n, where n is the number of required arguments and method created via defined_method
fails:Method#arity returns -(n+1), where n is the number of required arguments, when there is at least one optional argument
fails:Method#arity returns -(n+1), where n is the number of required arguments, when there is a splat argument, regardless of optional arguments
fails:Method#arity returns the same value regardless of the presence of a block
fails:Method#arity for a Method generated by respond_to_missing? returns -1
