Adding additional paths to Django's test runner

runners.py

from django.conf import settings
from django.test.runner import DiscoverRunner
import os

# You'll need to adjust those
SUBPATHS = ('myproject/apps', 'myproject/libs')
ROOT = dirname(dirname(dirname(os.path.abspath(__file__))))

class TestRunner(DiscoverRunner):
    """ Adds submodules from not-importable folders to the test suite.
        Works by adding those to the label list if building the suite
        of the whole project.
    """
    def build_suite(self, test_labels=None, extra_tests=None, **kwargs):
        test_labels, new_labels = test_labels or ['.'], []

        for label in test_labels:
            if label in ('myproject', '.'):
                new_labels.extend(self._generate_labels())
            else:
                new_labels.append(label)

        return super(TestRunner, self).build_suite(new_labels, extra_tests, **kwargs)

    def _generate_labels(self):
        """ Generate paths for all the modules we inject """
        dirname = os.path.dirname

        for subpath in SUBPATHS:
            path = os.path.join(ROOT, subpath)
            for item in os.listdir(path):
                itempath = os.path.join(path, item)
                if not os.path.isdir(itempath):
                    continue # module must be a folder
                if not os.path.isfile(os.path.join(itempath, '__init__.py')):
                    continue # module must be importable
                if item not in settings.INSTALLED_APPS:
                    continue # module must be active in Django conf
                yield os.path.join(path, item)

You would then add it to you Django settings, for instance:
TEST_RUNNER='myproject.core.runners.TestRunner'