testRTC is configured to terminate a test automatically after 5 minutes.
This is why if you try to run a long test, it will fail with this error message.
To resolve the issue, add #timeout:XXX to the run options of the test, where XXX stands for the number of minutes you want to allow.
You can learn more about timeout in testingRTC.
Typically, for long tests and/or stress tests, we recommend timeout to be set to 5 to 10 minutes more than the expected test time.
For a long running test (=over 15 minutes), be sure to follow our long running WebRTC test checklist.
The above example gives you up to 10 minutes for the test before it will be terminated.