Enhance kHeavyHash automated tests

This is a great first issue for someone interested in getting involved!

There are some basic kHeavyHash tests roughed in but there is significant room for improvement in this area. Since this is in the area of test code contributors can't break anything, but the possibility exists that you'll find a corner case that might be broken. In addition, you may find some ways to speed things up while learning about things.

We welcome your contributions! If this isn't yet assigned then it is available to work on.

Useful skills:

• C++ Programming is required, but this is test code so a great place to start learning.
• Understanding Boost Test stuff would be helpful or provide additional opportunity for learning.
• kHeavyHash fundamentals would be helpful, but not necessary.

Want to work on this issue?

For guidance on contributing, please read CONTRIBUTING.md before opening your pull request.