bug#51941: Detect duplication of ERT tests

[Mattias Engdegård]

24 nov. 2021 kl. 08.30 skrev Ihor Radchenko <yantar92@gmail.com>:

> This change breaks test code when a test file is "required" multiple
> times. In particular, Org mode tests cannot run with latest Emacs.

We'll have to do something about that then. Would you tell me more precisely 
what those Org tests do and why?
('require' is supposed to be idempotent; maybe you are missing a 'provide' 
somewhere?)