tl;dr A one-line fix for this common bug when updating an older Django project to Django 1.6+

After upgrading from Django 1.5 to Django 1.7 I came across the following warning whenever I started my local server:

?: (1_6.W001) Some project unittests may not execute as expected.
  HINT: Django 1.6 introduced a new default test runner. It looks like this project was generated using Django 1.5 or earlier. You should ensure your tests are all running & behaving as expected. See for more information.

The warning comes from the System Check Framework which is new in Django 1.7 and checks your project for common problems. You can run it manually with the “check” management command.

$	python check

So how to fix? The answer is you have to explicitly define a test runner starting in Django 1.6. So simply add the following single line to your settings file:

TEST_RUNNER = 'django.test.runner.DiscoverRunner'

Problem solved!