运行django教程测试失败 - 没有名为polls.tests的模块

我正在玩django 1.6教程,但我无法运行测试.我的项目(名称mydjango)和应用程序结构(名称是民意调查)如下所示在virtualenv中.(.nja文件只是由我正在使用的ninja-ide创建的)

.
??? __init__.py
??? manage.py
??? mydjango
?   ??? __init__.py
?   ??? __init__.pyc
?   ??? mydjango.nja
?   ??? settings.py
?   ??? settings.pyc
?   ??? templates
?   ?   ??? admin
?   ?       ??? base_site.html
?   ??? urls.py
?   ??? urls.pyc
?   ??? wsgi.py
?   ??? wsgi.pyc
??? polls
?   ??? admin.py
?   ??? admin.pyc
?   ??? __init__.py
?   ??? __init__.pyc
?   ??? models.py
?   ??? models.pyc
?   ??? templates
?   ?   ??? __init__.py
?   ?   ??? polls
?   ?       ??? detail.html
?   ?       ??? index.html
?   ?       ??? __init__.py
?   ?       ??? results.html
?   ??? tests.py
?   ??? tests.pyc
?   ??? urls.py
?   ??? urls.pyc
?   ??? views.py
?   ??? views.pyc
??? polls.nja

我按照教程了解django是如何工作的,但我陷入了测试部分.正如教程建议我在app文件夹中创建了一个名为tests.py的文件,非常简单的文件是:

# -*- coding: utf-8 -*-
from django.test import TestCase
import datetime
from django.utils import timezone
from polls.models import Question

# Create your tests here.l  
class QuestionMethodTests(TestCase):

    def test_was_published_recently_with_future_poll(self):
        """
        was_published_recently dovrebbe ritornare falso se si mette una data nel futuro
        """
        future_question = Question(pub_date=timezone.now() + datetime.timedelta(hours=50))
        self.assertEqual(future_question.was_published_recently(), False)

然后我将unittest2安装到virtualenv中

$pip install unittest2

并运行

$python manage.py test polls
Creating test database for alias 'default'...
E
======================================================================
ERROR: mydjango.polls.tests (unittest2.loader.ModuleImportFailure)
----------------------------------------------------------------------
ImportError: Failed to import test module: mydjango.polls.tests
Traceback (most recent call last):
  File "/home/sergio/.virtualenvs/django4/local/lib/python2.7/site-packages/unittest2/loader.py", line 260, in _find_tests
    module = self._get_module_from_name(name)
  File "/home/sergio/.virtualenvs/django4/local/lib/python2.7/site-packages/unittest2/loader.py", line 238, in _get_module_from_name
    __import__(name)
ImportError: No module named polls.tests


----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (errors=1)
Destroying test database for alias 'default'...

没有办法让测试工作,如果不传递应用程序名称,它返回相同的错误:

$ python manage.py test
Creating test database for alias 'default'...
E
======================================================================
ERROR: mydjango.polls.tests (unittest2.loader.ModuleImportFailure)
----------------------------------------------------------------------
ImportError: Failed to import test module: mydjango.polls.tests
Traceback (most recent call last):
  File "/home/sergio/.virtualenvs/django4/local/lib/python2.7/site-packages/unittest2/loader.py", line 260, in _find_tests
    module = self._get_module_from_name(name)
  File "/home/sergio/.virtualenvs/django4/local/lib/python2.7/site-packages/unittest2/loader.py", line 238, in _get_module_from_name
    __import__(name)
ImportError: No module named polls.tests


----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (errors=1)
Destroying test database for alias 'default'...

我的INSTALLED_APPS是:

INSTALLED_APPS = (
    'south',
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'polls',
)

我究竟做错了什么？