title: How to test async web services with PHPUnit?
body: <p>I am writing a test for a library which is a wrapper on an existing web service. Some of the calls of this web service are async: they ask for a callback url which they call when the processing is finished.</p>
  
  <p>What is the best way to test this with PHPUnit? Coming from other languages, my first idea is to spin up a web server as a part of the test and wait for the answer, but as far as I know this is not that easy in PHP.</p>
  
  <p>Is there a better way to do this?</p>