Describe the bug
Possibly related to #554 (reverted to v5.1.0-rc1 and they ran). Adding tests after starting to run tests (adding a test within a test) is not a supported pattern, and they won't actually get run (they do get added to the front of the individual list, but the merged test list doesn't not handle them).

To Reproduce
Add a unit test from within a unit test, build/execute and the added unit test will not execute.

Expected behavior
Didn't know NOT to do this... just don't do it.

Resolution
Just don't do it.
Document limitations and proper usage.

Code snips
uttest.c - see the adding and merging

System observed on:

• Hardware: cFS Dev Server
• OS: Ubuntu 18.04
• Versions checked latest integration candidate and v5.1.0-rc1, problem does not exist in v5.1.0-rc1

Additional context
#554

Reporter Info
Jacob Hageman - NASA/GSFC