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They're test cases for a compression library. Seems pretty reasonable.

Not at all. This would not pass a good code review. The test was for good stream, bad stream, good stream. The two good streams were only a few bites, why was the bad stream so large?

A good reviewer should have, even for a binary test case, asked the submitter to simplify it to the smallest or most basic binary required for the functionality.

idk picking a real-world example that breaks the code seems like a good test case to me

It is a good example for an initial bug report but, once the code has been fixed to handle that failure case, minimal examples are the correct lasting tests to live with the code forever.

Additionally, a complex example may require multiple conditions to fail and if those aren't split into multiple tests then subtle bugs can be reintroduced later because that complex test doesn't cover all potential failure conditions. If there need to be test cases for multiple related bugs then they need to be minimal to demonstrate the failure condition combinations they are testing for.

Adding a script to regenerate good and bad binary files might have worked for this use case pretty well too.

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