I was wondering why my NUnit tests were suddenly terminating successfully after 30 seconds whereas they usually take at least 20 minutes. Then I looked into the build log and found that after upgrading the mono version on our build agent to v 5.4.1, the test runner crashed with exit code 134.

After doing some research, I found out the following:
- The test runner works when using mono 4.8.1 (which we have installed, too), but the test code won't compile with it
- Ì also tried launching th erunner manually like so: `/Library/Frameworks/Mono.framework/Versions/5.4.1/bin/mono -v /Applications/TeamCity/buildAgent/plugins/dotnetPlugin/bin/JetBrains.BuildServer.NUnitLauncher.exe` which gave me the following error: `[1] 3461 abort /Library/Frameworks/Mono.framework/Versions/5.4.1/bin/mono -v` with the `3461`changing every time I retry.
- According to [this thread](https://ubuntuforums.org/showthread.php?t=1349120), exit code 134 means that the program crashed.

Due to the error output, I am not sure, whether it's the TeamCity test runner that crashes, mono that crashes or TeamCity that makes mono crash.

Any help appreciated :)