title: ImportError: No module named absl.testing
body: <p>I've been trying to run the <a href="https://github.com/tensorflow/models/blob/master/research/object_detection/g3doc/installation.md" rel="noreferrer">Object detection API</a>, at the point to test if the instalation worked: </p>
  
  <pre><code>python object_detection/builders/model_builder_test.py
  </code></pre>
  
  <p>I got the following error:</p>
  
  <pre><code>    File "object_detection/builders/model_builder_test.py", line 18, in &lt;module&gt;
      from absl.testing import parameterized
  ImportError: No module named absl.testing
  </code></pre>
  
  <p>I couldn't find a solution anywhere. Already tried <code>pip install absl-py</code> and <code>pip3 install absl-py</code> but without success.
  Hope you could help me.</p>