patch: it's now easier to populate data databases in test databases that run code in parallel

[Marcos Diez]

Although Django makes very easy for one to extend django.test.runner.DiscoverRunner , it's setup_databases() does too much.

Currently, it

• creates all the test databases (for single thread unit tests)
• duplicates all the test databases (in case of parallel unit tests)

In case I am running not running tests in parallel, I can just populate the DB after running unit tests without any issues.

But if I care about my time and want to run tests in parallel, I can either:

a) populate my data after setup_databases() is executed, once for each thread of the parallel tests, which is slow
b) get my hands dirty and reimplement setup_databases()

I propose (and I am sending the code to do so) a better solution. We just have to break setup_databases() in 3 functions:

DiscoverRunner.prepare_databases()
DiscoverRunner.populate_databases() # noop by default
DiscoverRunner.duplicate_databases_if_necessary()

The idea is quite simple: in order to be backward compatible, setup_databases() , will still exist but only call three functions above in that order.

The first function will create all the test databases necessary for non parallel tests to run.

populate_databases() , which should be a no op, can be overwritten by the user who extends django.test.runner.DiscoverRunner so his/her data can be populated

Afterwards, all the test DBs are copied as many times as necessary in case parallel tests are run via DiscoverRunner.duplicate_databases_if_necessary()

I believe this change on Django will have no downside, will be backward compatible and help people who needs to populate real data on the DB for their tests.