C++ Minimalistic Unit Testing Library
I decided I didn't want to use any of them. I decided to make my own.

That's a mistake.


and followed the convention of leading underscore to mean non-published.

A leading underscore followed by an uppercase letter is reserved identifier reserved for the implementation.

Please note that this code is published under the MIT license.

Also note that this code is not published under the creative commons license. See the bottom of the page. Everything published on any stack-exchange site is available under creative commons.
Design
There are a lot of missing features that I would expect in unit test framework.

Ability to run tests in isolation
Ability to run groups of tests.
Ability to set up state for tests
Ability to tear down state and reset the environment.
Some facility for mocking other classes.