contract-golden-test

Create a golden test that runs the round-trip build → serialize → validate → read in every consumer's gate, with all consumers importing one shared fixture set. Serializing with JSON.parse(JSON.stringify(x)) before validation is essential because the API only ever sees the wire payload.

Each consumer tests against its own local copy of the contract, so producer and assertion are internally consistent and stay green while the copies diverge. Only a round-trip test crossing a real package boundary catches the divergence between copies.

Validate after serialization. The save schema must check the wire form, because JSON serialization changes values like Date, undefined, Map, and class instances. Validating the in-memory object first lets exactly those divergences slip through.

No. The fixture set must live in exactly one package and be imported by every consumer. A copied fixture drifts together with the copy it sits next to, so the test then only confirms the local truth and becomes worthless.

It proves all copies speak the same form, not that the form is correct — a jointly wrong schema stays green. A new shim that forgets the shared fixture import is invisible to the test, and N consumers means N test runs for the same assurance.

Type-only tests using import type are erased at compile time, so the test merely asserts its own literals and stays green even after a field is deleted. The golden test must run at runtime against the real modules.