How often do your tests fail?
TL;DR A bit less often than yes, I have measured it.
In my case, I don’t commit all that often, but if you are building your code thousands of times per day, 99% confidence is probably not enough.
Why not have a little script to run them a number of times and see what happens? Here is mine:
Then I simply use it by running
./test-loop.sh 100 and wait for the
notification. If you are not on Ubuntu, you can replace
notify-send with your notification tool of choice. You
don’t need to do this often, but if you find your tests failing here and
there, better measure how often they actually fail.
My test suite takes about ~3 seconds to complete, so I can leave it running a few hundred times without wanting to die, but for bigger suites you probably want to avoid nondeterministic tests altogether.