Also, do test case reducers work on integers or other numbers? What about reducing some other complexity? Is this for developing unit tests or just debugging?
Imagine being handed a sheet of 10 equations and being told "1 of these equations is wrong." Now imagine that someone came in and erased 8 of the correct equations - they just saved you a bunch of time.
Similarly, narrowing test cases to the smallest case that reproduces a particular behaviour so you're only actually testing a very targeted thing will make the test suite faster and also make it easier to fix tests which break because they exercise a very narrow path.
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Boy I sure do wonder what character could possibly be causing issues there. whereas without shrinking it might instead spit out something like
ЁЂЃЄЅІЇЈЉЊЋЌЍЎЏАБВГДẞЕЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯабвгдежзийклмноп
Which makes finding the offending character a lot harder.