Allow to override TEST_RUNNER setting with a command-line option to 'manage.py 'test'

[Dmitry Jemerov]

In order to enable the integration of the Django test framework with IDE test runners, it's useful to be able to replace or decorate the test runner specified by the TEST_RUNNER setting in settings.py. Currently, the only way to do so is to provide our own settings.py which imports the user's settings.py and then changes the TEST_RUNNER setting. This is ugly and not always works.

A much preferred solution is to be able to override the test runner with a command line option passed to 'manage.py test'.

I've discussed this approach with russelm at the DjangoCon.EU sprint, and it was approved in general.

[Dmitry Jemerov]

Attached patch fixes this ticket along with ticket #15675 (it touches the same code so it's easier to fix both in the same patch)

[Ernesto Rico-Schmidt]

Patch looks good, it applies without problem. The tests pass.

[Russell Keith-Magee]

In [16352]:

Fixed #16185, #15675 -- Added the ability for test runners to define custom options, and to specify a custom test runner at the command line. Thanks to Dmitry Jemerov and Mikołaj Siedlarek for the patch.