title: verify that Zarr has been fully installed by running the test suite
body: <p>suggested cmds on Zarr:</p>
  <pre><code>$ pip install pytest
  $ python -m pytest -v --pyargs zarr
  </code></pre>
  <p>what I tried to make it work:</p>
  <pre><code>$ pip3 install pytest (succeeded)
  $ python3.7 pytest -v --pyargs zarr
  </code></pre>
  <p>Error I get</p>
  <pre><code>/Library/Frameworks/Python.framework/Versions/3.7/Resources/Python.app/Contents/MacOS/Python: can't open file 'pytest': [Errno 2] No such file or directory
  </code></pre>
  <p>I checked the path, and indeed the file <code>'pytest'</code> is somewhere else. Not sure if I may (and how) to change the path or location to make the cmd run</p>