fails:Kernel#instance_variable_defined? raises a TypeError if passed an Object not defining #to_str
fails:Kernel#instance_variable_defined? when passed a String returns false if the instance variable is not defined
fails:Kernel#instance_variable_defined? when passed a String returns true if the instance variable is defined
fails:Kernel#instance_variable_defined? when passed a Symbol returns false if the instance variable is not defined
fails:Kernel#instance_variable_defined? when passed a Symbol returns true if the instance variable is defined
