def check_test_runner():
    """
    Checks if the user has *not* overridden the ``TEST_RUNNER`` setting &
    warns them about the default behavior changes.

    If the user has overridden that setting, we presume they know what they're
    doing & avoid generating a message.
    """
    from django.conf import settings
    new_default = 'django.test.runner.DiscoverRunner'
    test_runner_setting = getattr(settings, 'TEST_RUNNER', new_default)
    if test_runner_setting == new_default:
        message = ["You have not explicitly set 'TEST_RUNNER'. In Django 1.6,",
            "there is a new test runner ('%s')" % new_default,
            'by default. You should ensure your tests are still all',
            'running & behaving as expected. See',
            'https://docs.djangoproject.com/en/dev/releases/1.6/#discovery-of-tests-in-any-test-module'
            , 'for more information.']
        return ' '.join(message)
