bug#51941: Detect duplication of ERT tests

[Ihor Radchenko]

Mattias Engdegård <mattiase@acm.org> writes:

> 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?)

In Org 9.5, we have test-oc.el. That file requires a macro defined in
test-ox.el:

In test-oc.el:
;; We need `org-test-with-parsed-data' macro.
(require 'test-ox "../testing/lisp/test-ox.el")

The load sequence is:
1. load-file test-oc
   1.1. test-oc requires test-ox
2. load file test-ox triggers error:
   Debugger entered--Lisp error: (error "Test ‘test-org-export/bind-keyword’ 
redefined")

Hope it helps.

Best,
Ihor