Projects

Testing a metaclass isn’t like testing a normal function — it fires when Python reads a class definition, not when you call it. This final post in the data-contracts series covers everything: autouse fixtures for global state isolation, testing metaclass behaviour by its observable outcomes, parametrize for every change type, and the heuristic edge cases…

Not all schema changes are equal. A new field is safe — consumers ignore it. A renamed field is breaking — consumers expecting the old name will fail silently. This post walks through how SchemaDiff classifies every change, how the rename heuristic works, and how the NotificationBus alerts only the teams that need to know.

When you inherit from ContractBase, three things happen automatically — registration, field extraction, and validation — before the next line of your code runs. This post explains exactly how: the MRO walk, why get_type_hints() beats __annotations__, closures, and the schema registry that ties it all together.

One field rename. 50 broken pipelines. No warning. Here’s how I built a Python framework that detects breaking schema changes automatically — before they reach production.