title: long running py.test stop at first failure
body: <p>I am using <a href="https://docs.pytest.org/en/latest/" rel="noreferrer"><code>pytest</code></a>, and the test execution is supposed to run until it encounters an exception. If the test never encounters an exception it should continue running for the rest of time or until I send it a SIGINT/SIGTERM.</p>
  
  <p>Is there a programmatic way to tell <code>pytest</code> to stop running on the first failure as opposed to having to do this at the command line?</p>