The kata description first says that PublicField is a string, but then in the first example (valid use) it uses PublicField as a number.
I found it somewhat confusing. I thought that the tests could have tried to do such numerical operations, so I thought of unnecessarily complicated solutions such as making a getter for PublicField which would have returned an Int32.TryParse.
I think that it would be best if you changed the example to avoid confusion.

Apart from that I enjoyed the kata. Nice job, thank you.