Testing is an extremely inadequate measure of reliability and robustness.
Tests can show you problems, if you can find them, but they cannot show that there are no problems. Property based testing or fuzzing gets your more coverage, and is a good step, but it is still nothing compared to proving things or understanding how something is built and that it is solid. Testing works towards checking for reliability and robustness, but often it's only 10% (?) of the job.
I'm curious - is there any data on the Bun port error rate? I think that would be very indicative of how successful or not the testing is.