Testmods don't check that folder contains valid testmods

I recently made a typo when submitting a test, which got undetected. I had some testmods in a fews subfolders of a main folder. Let's call the parent folder "root" and the subfolders "1", "2', and so on. The correct testmod were then `.root-1`, `.root-2`, and so on. However, I accidentally just typed `.root`. Since the "root" folder existed, CIME did not complain. However, it also did not add any testmod, since no `shell_commands` was in that folder (nor any `user_nl_XYZ`).

I think it would be nice if CIME checked that the testmod _does something_, precicely to avoid cases where the user specifies only part of the path/to/testmod. This could be implemented either as an error or warning, depending on how sure we are that not finding valid mods is indeed an error rather than "a coincidence" (maybe inside some general purpose script). But having at least a warning would allow one to see in the logs that a testmod they tought was added was not indeed added.