title: Request headers in APITestCase
body: <p>I have a test (<code>APITestCase</code>), and I need to specify custom headers:</p>
  
  <pre><code>class ListAppsAPITest(APITestCase):
      def test_list_apps_versions(self):
          response = self.client.get(reverse('api:applications:list'), None, **{'Device-Id': 'deadbeef'})
  </code></pre>
  
  <p>I've tried different combinations of arguments, but it did not work.</p>
  
  <p>How to specify custom headers in tests?</p>