The only real advantage of adding a native unit testing framework here is to avoid having to start/destroy _testembed[.exe] multiple times during the test run. But given the nature of these tests is highly environmental, I don't think we can reasonably avoid it. I'm also highly doubtful that any framework is going to actually reduce the work we'd need to do to mock out initialization steps.

I've attached a patch that takes the first step towards making _testembed more usable, by changing main() to look up a test from a list and execute it, then return the exit code. The support in test_capi.EmbeddingTests is neat, so adding more tests here will be fairly straightforward.