Document how to avoid running certain test classes in parallel

[Tobias Krönke]

In PR ​https://github.com/django/django/pull/9342 I propose to enable users to mark tests for non-parallel execution. In this way, they don't have to make sure, that all their tests are properly isolated. This is useful, if you work with other external storages like e.g. solr and django-haystack.

[Tim Graham]

Isn't this is already provided by ba813864870d63de1d1679271c38a3c15e94e934? It could probably be documented if needed.

[Tobias Krönke]

I don't want to be too eager for this to be merged. I probably wouldn't have looked any further had I known this Mixin. Still I would like to point out some advantages of my solution:

• Less complex to use
• Less complex implementation (especially no lock files involved)
• More efficient, if you have only 1 shared resource (no concurrent waits for the locked file)

Of course I also see the advantage of the existing mixin, that you can use different lock files for different shared resources if you have many. A hint in the docs would be quite pleasant.

So, your call ;-)

[Tim Graham]

I guess it's better to document the existing class rather than add another one unless the new implementation is preferred for some reason.

[Caio Ariede]

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In dafdfd6a:

Fixed #28790 -- Doc'd how to avoid running certain test classes in parallel.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 7d8d2b56:

[3.0.x] Fixed #28790 -- Doc'd how to avoid running certain test classes in parallel.

Backport of dafdfd6a60638c4edcca7c4e65d11c0af654d759 from master

[Mariusz Felisiak <felisiak.mariusz@…>]

In 5e91adc7:

[2.2.x] Fixed #28790 -- Doc'd how to avoid running certain test classes in parallel.

Backport of dafdfd6a60638c4edcca7c4e65d11c0af654d759 from master