Evidence for a rule
Build discriminating cases, input partitions and checkable preservation properties.
Write a preservation rule beyond a few good examples
Turn observed examples into a checkable invariant without claiming universal proof.
Choose examples from different validity groups
Cover distinct input classes before adding more similar successful examples.
Cover combinations rather than listing each input once
Build a small matrix for independent dimensions that interact in the result.
Check a rule by reordering independent input records
Specify a relationship between two runs when each record is evaluated independently.
State what a successful edit must leave unchanged
Add preservation checks beside the intended changed value.