python - How to run Django's test database only in memory?

Question

My Django unit tests take a long time to run, so I'm looking for ways to speed that up. I'm considering installing an SSD, but I know that has its downsides too. Of course, there are things I could do with my code, but I'm looking for a structural fix. Even running a single test is slow since the database needs to be rebuilt / south migrated every time. So here's my idea...

Since I know the test database will always be quite small, why can't I just configure the system to always keep the entire test database in RAM? Never touch the disk at all. How do I configure this in Django? I'd prefer to keep using MySQL since that's what I use in production, but if SQLite 3 or something else makes this easy, I'd go that way.

Does SQLite or MySQL have an option to run entirely in memory? It should be possible to configure a RAM disk and then configure the test database to store its data there, but I'm not sure how to tell Django / MySQL to use a different data directory for a certain database, especially since it keeps getting erased and recreated each run. (I'm on a Mac FWIW.)

Answer 1

If you set your database engine to sqlite3 when you run your tests, Django will use a in-memory database.

I'm using code like this in my settings.py to set the engine to sqlite when running my tests:

if 'test' in sys.argv:
    DATABASE_ENGINE = 'sqlite3'

Or in Django 1.2:

if 'test' in sys.argv:
    DATABASES['default'] = {'ENGINE': 'sqlite3'}

And finally in Django 1.3 and 1.4:

if 'test' in sys.argv:
    DATABASES['default'] = {'ENGINE': 'django.db.backends.sqlite3'}

(The full path to the backend isn't strictly necessary with Django 1.3, but makes the setting forward compatible.)

You can also add the following line, in case you are having problems with South migrations:

    SOUTH_TESTS_MIGRATE = False