As already mentioned in my comment, there is a regression caused by #403 which prevents the exit code from being set in time, which causes the process not to fail in case the coverage threshold is not met.

I've created a small example to show-case the current behavior and also did some PoC on how it might be solved:
https://github.com/matz3/issue-karma-coverage-threshold-exit-code

Here are the changes to karma and karma-coverage

• feat(server): allow 'exit' listeners to set exit code karma#3541
• fix(reporter): set exit code when thresholds aren't met #420

With v2.0.1 everything seems to work fine.