Programs/_testembed (invoked by test_capi to test CPython's embedding support) is currently a very simple application with only two different embedding tests: https://hg.python.org/cpython/file/tip/Programs/_testembed.c

In light of proposals like PEP 432 to change the interpreter startup sequence and make it more configurable, it seems desirable to be better able to test more configuration options directly, without relying on the abstraction layer provided by the main CPython executable.

The specific unit testing library that prompted this idea was cmocka, which is used by libssh, sssd and cwrap: https://cmocka.org/

cwrap in turn is used by the Samba team to mock out network interfaces and other operations using LD_PRELOAD: https://cwrap.org/

We don't necessarily have to use those particular libraries, I'm just filing this issue to capture the idea of improving our C level unit testing capabilities, and then updating regrtest to better capture and report those results (currently there are just a couple of tests in test_capi that call the _testembed executable)