How to test django using test sqlite3 database instead default mysql database?

Question

My databases in settings.py

'default': {
    'ENGINE': 'django.db.backends.mysql',
    'NAME': 'dbname',
    'USER': 'user',
    'PASSWORD': 'password',
    'HOST': 'mydb.com',
    'TEST': {                                        # it's not works
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': ':memory:',
    }
}

But TEST section not work.

I use this code and it works but i don't like it. Maybe there are other way in databases section describe test database?

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