title: In what Thread do XCUnitTestCases run?
body: <p>I am testing a method, that uses a <code>Geocoder</code>. To make the test synchronous, I mocked the <code>Geocoder</code>, so that I can directly call the <code>completionHandler</code> inside my Unit-Test where needed.</p>
  
  <p>This worked perfectly fine, until I introduced a code block in <code>Geocoder</code>'s <code>completionHandler</code> that runs on the main thread. (<code>DispatchQueue.main.async {}</code>). </p>
  
  <p>I then noticed, that my Unit-Test does not pass anymore, as the assertions are called before the <code>DispatchQueue.main.async{}</code> block. I solved it by using expecations. </p>
  
  <p>However, this made me wonder whether XCUnitTestCases run on a different thread than the main thread. I did not find anything in the documentation about this.</p>