如何在测试中使用Django的反向解析？

我不知道如何在Django中使用反转函数。我得到了这个错误信息：ValueError: 字典更新序列元素＃0的长度为1，而需要2。我可以直接硬编码URL，这样可以正常工作，但我希望以标准方式完成。

主urls.py

urlpatterns = [
            url(r'^nmailadmin/', admin.site.urls),
            url(r'^api/v1/',include('Core.Login.urls',namespace='login')),
            url(r'^api/v1/mail/',include('Core.Mail.urls',namespace='mail')),
 ]

我为登录和邮件API设置了命名空间。当我尝试访问邮件URL时，如下所示：

def test_0list_folders(self):
    url = reverse('mail:folder_list', kwargs={'server':0})
    response = self.client.get('/api/v1/mail/folder_list/0/', follow=True)
    self.assertEqual(status.HTTP_200_OK, response.status_code)

我得到了以下错误：

----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/next/PycharmProjects/Nmail/Nmail-Server/Core/Mail/tests.py", line 25, in test_0list_folders
    url = reverse('mail:folder_list', kwargs={'server':0})
  File "/home/next/venv/NmailVenv/lib/python3.6/site-packages/django/urls/base.py", line 91, in reverse
    return force_text(iri_to_uri(resolver._reverse_with_prefix(view, prefix, *args, **kwargs)))
  File "/home/next/venv/NmailVenv/lib/python3.6/site-packages/django/urls/resolvers.py", line 436, in _reverse_with_prefix
    self._populate()
  File "/home/next/venv/NmailVenv/lib/python3.6/site-packages/django/urls/resolvers.py", line 309, in _populate
    dict(defaults, **pattern.default_kwargs),
ValueError: 字典更新序列元素＃0的长度为1，而需要2
----------------------------------------------------------------------

这是我的邮件应用的urls文件。

urlpatterns = [
   url(r'folder_list/(?P\d+)/$', folder_list,name='folder_list'),
   url(r'^auth_login/$', login_auth, name='auth_login'),
   url(r'viewmsg/(?P\d+)/(?P.*?)/(?P\d+)/$', viewmsg, name='viewmsg'),
    url(r'action/(?P.*?)/$', action, 'action'),
     ]

Django版本：Django==1.11.7