Improve Python unit tests

[thibaudcolas]

• [ ] Do they need a DB?
• [ ] Add test-watch command. The one in draftjs_exporter is based on nodemon. Perhaps there is a more sanctified way to do this with Django tests.
• [ ] Prevent fast failure – we want to see all the fails in the test suite.
• [ ] Get rid of that big useless stack trace.

[loicteixeira]

If you need a Django model, then yes you need a db. And if you don't care about the database to stick around, you can use an in-memory sqlite db for the tests.

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': ':memory:'
    }
}

[thibaudcolas]

Well that is perfect. Thank you Loïc!