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How do you know whether random testing is working as expected? [1/3] Long ago in JQF, we used `assumeTrue` to bias fuzzing towards *valid* inputs. This is powerful, but the abstraction is quite coarse if you have many properties. (Refs: github.com/rohanpadhye/..., rohan.padhye.org/files/zest-i...)

[2/3] I like the "Sometimes Assertions" abstraction recommended by Antithesis, which generalizes code coverage to user-defined predicates, possibly interleaved with application logic. Maybe we should support these in JQF too. (Ref: antithesis.com/docs/best_pr...)

Takeaway: Don't just fuzz and wait for bugs to show up. Measure what your inputs look like based on user-defined predicates, and things start making a lot more sense.