dbt Analytics Engineering Certification

Model contracts support SQL models, not Python models, and a preflight check can detect column-name or data-type mismatches before materialization. Data tests can be configured to return warnings or errors and can test ephemeral models, which do not support contracts. (docs.getdbt.com)

The first two distinctions apply to data tests rather than all tests: unit tests currently support SQL models and can run before a model is materialized. (docs.getdbt.com)