Short answer: Stubs are a code-level description of the responses; contract tests verify the responses against the schema. The first tells the mock what to return; the second proves the real response is valid. They are different stages and both belong in a pipeline.
What stubs provide
Controlled responses for the tests, so the system can be exercised without the real service. They are authored and can drift.
What contract tests provide
| Property | Stubs | Contract tests |
|---|---|---|
| Subject | Mock responses | Real responses |
| Authority | Stub code | Schema |
| Catches drift | Not directly | Yes |
| Stage | Isolation | Verification |
Why the stages matter
A stub lets the system run without the dependency; a contract test proves the dependency still conforms. Replacing one with the other leaves a gap.
The honest takeaway
Keep the stubs for isolation and the contract checks for conformance. A spec-first studio keeps both tied to the same source.
This is part of the Powerduck vs WireMock comparison. Next, read beyond JVM mocking.
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