Testing

Mutating structure, not bytes: nelli's IR-aware fuzzing

I expected byte mutation to lose because its mutants die at the decoder. Measured, they decode fine. About 83% of them decode to the value you already had. nelli mutates the typed choice sequence instead, and reaches 18 edges of a parser where byte mutation reaches 2.

nelli: one engine for property testing, fuzzing, and symbolic execution

nelli is a Nim testing library built on a choice-sequence engine. Because a test input is just a recorded sequence of typed choices, the same engine drives property testing, coverage-guided fuzzing, and SMT-backed symbolic execution.

Deciding to lock your screen should be a pure function

PresenceLock locks your Windows session when you step away from the webcam. Twice it silently stopped locking while reporting that it was watching. Both bugs were caught, and both fixes were possible, because the decision to lock is a pure F# function with no clock and no I/O.