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.

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)?