So, since this is basically a private class, you are effectively testing implementation details here. However, as long as you have a checkbox example in the generated specs, this would be uneccessary.

As a rule of thumb, if you are testing implementation details or stubbing internal things either, there is a better spec to write on an existing public interface, or your interface is wrong.

If you are having a hard time writing specs, it is a good indication that something in your interface or implementation is probably not right.