In my opinion it should only be a duplicate, if the instance is of the same class and all instance variables are set to the same value. What is the definition of "duplicate" here? What instance is a duplicate in the test case according to the maker of this kata?

I would say, the task should be explained as "counting ones in the base 2 representation" (or something like that).

My code works if I escape the ' in the input (aren't).
In the input here, the ' character is not escaped. How can I fix this problem?