title: Postgres function json_array_elements does not found while django's tests
body: <p>I have class method in django model which is using <code>json_array_elements</code> function.</p>
  
  <p>In case when it performs by browser it works fine.
  But in tests it fails.
  <code>python manage.py test</code></p>
  
  <pre><code>Traceback (most recent call last):
    File "path_to_project/dj_server/model_animations/tests.py", line 94, in test_cteating
      response_first = model_animations.views.get_animations_list(request, groupid)
    File "path_to_project/dj_server/model_animations/views.py", line 37, in get_animations_list
      for model_anim in listArray:
    File "/Library/Python/2.7/site-packages/django/db/models/query.py", line 1535, in __iter__
      query = iter(self.query)
    File "/Library/Python/2.7/site-packages/django/db/models/sql/query.py", line 76, in __iter__
      self._execute_query()
    File "/Library/Python/2.7/site-packages/django/db/models/sql/query.py", line 90, in _execute_query
      self.cursor.execute(self.sql, self.params)
    File "/Library/Python/2.7/site-packages/django/db/backends/utils.py", line 65, in execute
      return self.cursor.execute(sql, params)
    File "/Library/Python/2.7/site-packages/django/db/utils.py", line 94, in __exit__
      six.reraise(dj_exc_type, dj_exc_value, traceback)
    File "/Library/Python/2.7/site-packages/django/db/backends/utils.py", line 65, in execute
      return self.cursor.execute(sql, params)
  ProgrammingError: function json_array_elements(text) does not exist
  LINE 1: ...on_name FROM model_animations_model, json_array...
                                                               ^
  HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
  </code></pre>
  
  <p><strong>in models.py</strong></p>
  
  <pre><code>@classmethod
  def animations_list(self, group_id):
      if group_id:
          try:
              listArray = ModelAnimationList.objects.raw(('SELECT * FROM model_animations_model, json_array_elements(animated_groups) AS data WHERE \'"%s"\' = data::text' %group_id))
              return listArray
          except:
              pass
      return None
  </code></pre>
  
  <p><strong>in views.py</strong>
  def get_animations_list(request, group_id):
      ...</p>
  
  <pre><code>listArray = ModelAnimationList.animations_list(group_id)
  if listArray:
      for model_anim in listArray:
          if model_anim:
              anim_dict = { 'a_id'  : model_anim.id, 'a_name' : model_anim.animation_name }
              result_anim_list.append(anim_dict)
  
  ...
  </code></pre>
  
  <p><strong>in tests.py</strong></p>
  
  <pre><code>request = HttpRequest()
  response_first = model_animations.views.get_animations_list(request, groupid)
  </code></pre>
  
  <p>Installed: <br/>
  python 2.7 <br />
  Django 1.7.1 <br />
  Postgres 9.3.5 <br />
  psycopg2 2.5.4 <br />
  Mac 10.10 yosemite</p>