      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)
  
 
</s> remove         self.assertTrue("You have not explicitly set 'TEST_RUNNER'" in check.warnings._warnings[0])
 </s> add         self.assertTrue("Django 1.6 introduced a new default test runner" in check.warnings._warnings[0]) </s> remove             self.assertTrue("You have not explicitly set 'TEST_RUNNER'" in result)
 </s> add             self.assertTrue("Django 1.6 introduced a new default test runner" in result) </s> remove             self.assertTrue("You have not explicitly set 'TEST_RUNNER'" in result[0])
 </s> add             self.assertTrue("Django 1.6 introduced a new default test runner" in result[0]) </s> remove             self.assertTrue("You have not explicitly set 'TEST_RUNNER'" in result[0])
 </s> add             self.assertTrue("Django 1.6 introduced a new default test runner" in result[0])
            "Django 1.6 introduced a new default test runner ('%s')" % new_default,
            "You should ensure your tests are all running & behaving as expected. See",
      test_runner_setting = getattr(settings, 'TEST_RUNNER', new_default)
  
      if test_runner_setting == new_default:
          message = [
            "Django 1.6 introduced a new default test runner ('%s')" % new_default,
            "You should ensure your tests are all running & behaving as expected. See",
            "Django 1.6 introduced a new default test runner ('%s')" % new_default,
            "You should ensure your tests are all running & behaving as expected. See",
            "Django 1.6 introduced a new default test runner ('%s')" % new_default,
            "You should ensure your tests are all running & behaving as expected. See",
            "Django 1.6 introduced a new default test runner ('%s')" % new_default,
            "You should ensure your tests are 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)
  
keep keep keep keep replace replace replace replace keep keep keep keep keep
 Refs #21197 -- Clarified upgrade check message.

Thanks to Carl and Shai for the discussion. 
django/core/checks/compatibility/django_1_6_0.py