[funstuff007]

fair enough, but few things are easier to test than a regex.

[russfink]

Few things are easier to miss than a string that breaks your (nontrivial) regex.

I’d like to see a mathematical estimate of the number of test strings I should generate given some input regex.

[funstuff007]

If you cannot enumerate the test cases, then the problem is too complex for a single regex. It's sort of self limiting.