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.
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.