Opinion: Your Tests Can't See What a Migration Destroys — Dry-Run It on a Clone
A green test suite is the wrong tool for judging an AI-generated migration, because tests run against the post-migration schema and never observe the intermediate states where data disappears. The up migration is the visible artifact that gets reviewed, while the down migration is treated as an afterthought even though it is the only safety net when the deployment goes wrong. Free model access makes the problem structural: generation cost drops to zero, so migration volume rises, and every additional migration multiplies the surface for unreviewed data loss. Disclosure: This article was prepared as part of MonkeyCode's product outreach.
Tests validate the destination, not the journey
When a test suite runs against a migrated database, it confirms that the application can read the new schema, but it cannot confirm that the migration preserved the data it was supposed to preserve. The test runner connects after the migration has executed, so it never sees the moment when a column is dropped, a table is renamed, or a constraint is silently relaxed. A migration that passes every test can still destroy production data, because the tests were designed to validate application behavior, not migration safety.
