Setting DATABASES['default']['TEST']['engine'] to SQLite does not cause Django to use an in-memory database as expected

[mrts]

Preconditions

Given the following settings:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': 'database',
        ...
        'TEST': {
            'ENGINE': 'django.db.backends.sqlite3',
        }
    }
}

Actual

When I run ./manage.py test in a restricted environment, then I get the following error:

$ ./manage.py test
Creating test database for alias 'default'...
Got an error creating the test database: permission denied to create database

Type 'yes' if you would like to try deleting the test database 'test_database', or 'no' to cancel: yes
Destroying old test database 'default'...
Got an error recreating the test database: database "test_database" does not exist

Expected

The documentation says:

The default test database names are created by prepending test_ to the value of each NAME in DATABASES. When using SQLite, the tests will use an in-memory database by default (i.e., the database will be created in memory, bypassing the filesystem entirely!).

Thus, my expectation was that setting DATABASES['default']['TEST']['engine'] to SQLite will use an in-memory database.

[mrts]

There is a workaround documented here:

​https://stackoverflow.com/a/3098182/258772

But this is complex and fragile.

[Tim Graham]

'ENGINE' ​isn't a supported option in 'TEST':

Aside from using a separate database, the test runner will otherwise use all of the same database settings you have in your settings file: ENGINE, USER, HOST, etc.

You should use a separate settings file when testing if you want to use a different database backend.

[mrts]

Replying to Tim Graham:

'ENGINE' ​isn't a supported option in 'TEST':

Aside from using a separate database, the test runner will otherwise use all of the same database settings you have in your settings file: ENGINE, USER, HOST, etc.

You should use a separate settings file when testing if you want to use a different database backend.

Thanks for clarifying! This is not clear from the documentation section that you referred to. Should I submit a documentation patch?

[Tim Graham]

I'm not sure if clarification is required. The sentence is clear to me and there's no documentation for a TEST['ENGINE'] setting.

[mrts]

Alright, let's leave it as is then. Thanks for helping!