How a Migration Contract Can Catch Data Bugs That Code Review Misses

Database migrations that appear correct during code review can still corrupt data by failing to handle edge cases such as single-word or multi-word names. A name-splitting migration, for example, may leave empty first-name fields or silently drop middle names for affected rows. The proposed approach treats each migration as a verifiable contract by defining preconditions, invariants, and rollback conditions before any code runs. A lightweight test harness using SQLite and an in-memory database can validate these claims against deliberately malformed seed data, catching logic errors cheaply and early. The article demonstrates this with a flawed Python script where an assertion correctly flags a one-word name record, proving the contract-based method surfaces bugs that a simple script review would miss.