Datamimic makes a coding agent prove its test-data model before the data exists.

Datamimic generates byte-identical synthetic test data for the same seed, and its agent workflow is the notable bit: the agent preserves intent as JSON, submits a scaffolding request via CLI, gets machine-readable validation diagnostics, and repairs the model until it reports verified=true. That's a concrete gate for the common failure where an agent writes tests against a fixture world it invented and they pass for the wrong reason.