Is there an expression in programming that something will 'exercise bugs'?
I have seen this written before but I don't know what it means.
Exercising bugs would be a pointless activity. What you would do instead is exercise the program to uncover bugs.
You can do this a number of different ways:
Integration tests are a form of exercising code. Unit tests tend to operate in a "sterile lab" environment; running the code in its normal working environment can uncover bugs that didn't appear during unit testing.