Adding unit tests for net.authorize.sample.Sha512.ComputeTransHashS512

[EdgarScott]

I've analysed your codebase and noticed that net.authorize.sample.Sha512.ComputeTransHashSHA512 is not fully tested. I've written some tests for this class with the help of Diffblue Cover.

Hopefully, these tests will help you detect any regressions caused by future code changes. If you would find it useful to have additional tests written for other classes, I would be more than happy to look further.