Strategy

A spec gives three different things to check, so the generator emits three layers of tests, each aimed at a class of defect the others miss. Together they carry conformance from "the API has the right shape" to "the API keeps its contract across a run."

The structural layer comes first because it is the cheapest signal. Schemathesis fuzzes the generated OpenAPI surface, throwing malformed and boundary inputs at every endpoint and checking that the response is a declared status with a schema-valid body. It proves the API has the right shape, not the right values. The behavioral layer takes that on: from each operation's requires and ensures it builds Hypothesis property tests that drive one operation and assert its postcondition, so a single call is held to its contract. What that still cannot see is a sequence of calls drifting off the invariants, and the stateful layer is the sequence test, a Hypothesis state machine that drives operation orderings against a model of the spec's state and checks the global invariants after each step. Each layer is aimed at exactly what the one before it cannot reach.

The three layers hold for every target; only the tools change, Schemathesis and Hypothesis on Python, Vitest and fast-check on TypeScript, go test and rapid on Go. The exact files each layer emits, and the conformance runner that stands the service up and runs them, are on the test-generation pipeline page.