Use django build-in test runner

setup.py

@@ -1,7 +1,17 @@
+import sys
 from setuptools import find_packages, setup
+import os
 
 from django_mailbox import __version__ as version_string
 
+os.environ['DJANGO_SETTINGS_MODULE'] = 'django_mailbox.tests.settings'
+
+from django.core import management
+
+if sys.argv[-1] == 'test':
+    management.execute_from_command_line()
+    sys.exit()
+
 tests_require = [
     'django',
     'mock',