Move c++ tests to Google Test

[mikebentley15]

Feature Request

Describe the new feature:
I rolled my own testing framework, which works really well from a single header file, but may not be as standardized as something like Google Test. There may be benefits (like utilizing automated dashboard services for automated tests) to switching to Google Test.

Suggested change:
Remove test_harness.h and replace it with the use of Google Test. The documentation would need to be updated to reflect that the Google Test framework is a dependency if you want to run tests.

Alternative approaches:
There are other good testing frameworks out there.

We could alternatively extend our framework to behave like Google Test. I don't like that idea though.