Not mutation testing — nothing is mutated. It builds both branches with instrumentation, runs the same test suite on each, and diffs the recorded arguments and return values. In that example, selectDiscount returns a different discount and the order total goes 85 → 60. Neither function is in the diff; only the sort helper is. The tests still pass — one asserts the total is positive, and 60 is positive.

Don’t run your responses through an LLM. People prefer to read your genuine words, even if it may include some incorrect English.

Sure, appreciate the feedback.

please try speaking in your own words. i still have no idea what this is for. is it two compare two impls? is it to "optimize" a function (i assume not since there's no mutation)?

hi, this is simply put, to compare the behavior diff of two builds. when i say behavior, i mean the return values of functions etc. it'll help with AI-assisted code reviews etc. since AI looks at the text diff only, and misses behavior diff downstream. it complements static analysis and unit tests for a stronger testing strategy.