TestRunner playmode timeout (?)

Hi all,

Question:
Does the TestRunner feature (Unity 5.6) have a timeout setting somewhere? And if so, then where can I deactivate it?

Context:
Using the TestRunner to run tests in PlayMode (coroutine-alike) my test so far always terminate (pass) prematurely after about 30 seconds.
(I need my test runs to run considerably longer in order to test complex gameplay scenarios.)

Code:
Here is a snippet that reliably produces the phenomenon for me:

 using UnityEngine;
 using UnityEngine.TestTools;
 using NUnit.Framework;
 using System.Collections;
 public class TestingTest 
 {
     // A UnityTest behaves like a coroutine in PlayMode
     // and allows you to yield null to skip a frame in EditMode
     [UnityTest]
     public IEnumerator TestingTestWithEnumeratorPasses() 
     {
         float timeIntervalReport = 1;
         float timeReportLast = 0;
         float durationDesired = 40;
         
         float timeStart = Time.time;
         Debug.Log("timeStart " + timeStart);
         
         while(Time.time < timeStart + durationDesired){
             if(timeReportLast + timeIntervalReport < Time.time){
                 Debug.Log("time passed " + (Time.time - timeStart));
                 timeReportLast = Time.time;
             }
             yield return null;
         }        
         Debug.Log("test complete");
     }
 }

Thanks for your consideration.