Individual skill
mock-stub-designer
Designs the minimal set of test doubles for a unit or integration test and decides, per dependency, whether to stub, fake, spy, mock, or exercise the real thing. Use when someone asks "should I mock this", "how do I test code that calls Stripe or S3 or the clock", "why do our tests pass while production is broken", or when a test touches an HTTP API, payment or email/SMS SDK, database, filesystem, system clock, or randomness. Do NOT use for fabricating valid domain fixture data (a User with defaults, an Order with line items) - use test-data-builder instead; for driving a red-green implementation loop, use tdd-expert.
skills/mock-stub-designer/SKILL.md
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- claude Repository topic
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# Mock Stub Designer
A test double exists to make a test fast, deterministic, and focused - never to mock everything in sight. Over-mocking yields tautological tests that pass against a broken system because they only verify the mocks. This skill decides, per dependency, the weakest double that still isolates the boundary, so the test exercises real behavior everywhere else.
## Operating procedure
### Step 1: Gather inputs
Collect before designing anything:
1. The unit under test and the behavior being verified (one sentence).
2. Every dependency the code touches, direct and transitive-at-the-boundary: HTTP/third-party APIs, payment/email/SMS SDKs, database, filesystem, clock, randomness, queues.
3. Language and test stack (this picks the wire-interception tool: nock or msw for JS, WireMock for JVM, VCR-style cassettes for Ruby/Python, responses/respx for Python).
4. Whether a sandbox environment exists for the critical integration backstop.
