Turns the acceptance criteria a task states into executable checks and runs them against the finished outputs before delivering, rather than trusting that a correct-looking analysis satisfies them; rehearses the hidden condition when the grader scores unseen instances from a described family; treats a stated formula, update rule or predicate as the oracle to implement first; so that every stated path, schema, unit, rounding rule, ordering, tolerance, threshold, named method and version, prescribed heading and self-consistency formula becomes a small test, any checker the task ships is run as the exit criterion, derived quantities are recomputed from the primitives, and conventions such as units, signs, coordinate frames and code tables are transcribed into named functions with hand-checked cases. Use whenever a task states how the result will be judged mechanically, ships a validation script, or specifies output formats and tolerances; a report a reader grades needs only its headings and files checked once, and free-form exploration with no stated criteria does not need it.