title: RuntimeWarning: coroutine was never awaited in tests
body: <p>I'm trying to test a async Python function using pytest. My test is passing with a warning, when it <em>should</em> be failing.</p>
  
  <p>This is my test:</p>
  
  <pre><code>import asynctest
  import pytest
  
  from Foo.bar import posts
  
  @pytest.mark.asyncio
  async def test_get_post_exists():
      returned_post = await posts.get_post('0')
  
      assert returned_post.id == 0
      assert returned_post.text == 'Text for the post body.'
      assert True == False
  </code></pre>
  
  <p>It passes with the following message:</p>
  
  <pre><code>================================== test session starts ===================================
  platform darwin -- Python 3.6.4, pytest-3.4.2, py-1.5.2, pluggy-0.6.0
  rootdir: /path/path/path/path, inifile:
  collected 1 item
  
  tests/unit/route_logic/test_post_helpers.py .                                      [100%]
  
  ==================================== warnings summary ====================================
  tests/unit/route_logic/test_post_helpers.py::test_get_post_exists
    /usr/local/lib/python3.6/site-packages/_pytest/python.py:155: RuntimeWarning: coroutine 'test_get_post_exists' was never awaited
      testfunction(**testargs)
  
  -- Docs: http://doc.pytest.org/en/latest/warnings.html
  ========================== 1 passed, 1 warnings in 0.10 seconds ==========================
  </code></pre>