Matt Pocock
62f43a1817
- Introduced TDD skills including deep modules, interface design, mocking, refactoring, and testing guidelines. - Added skills for breaking plans into GitHub issues and creating PRDs from conversation context. - Implemented productivity skills for scaffolding exercises, setting up pre-commit hooks, and managing notes in Obsidian. - Created a caveman communication mode for concise technical responses and a grilling technique for thorough plan discussions. - Developed a skill for writing new agent skills with structured templates and guidelines. - Included git guardrails to prevent dangerous git commands and a migration guide for using @total-typescript/shoehorn in tests.
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Deepening
How to deepen a cluster of shallow modules safely, given its dependencies. Assumes the vocabulary in LANGUAGE.md — module, interface, seam, adapter.
Dependency categories
When assessing a candidate for deepening, classify its dependencies. The category determines how the deepened module is tested across its seam.
1. In-process
Pure computation, in-memory state, no I/O. Always deepenable — merge the modules and test through the new interface directly. No adapter needed.
2. Local-substitutable
Dependencies that have local test stand-ins (PGLite for Postgres, in-memory filesystem). Deepenable if the stand-in exists. The deepened module is tested with the stand-in running in the test suite. The seam is internal; no port at the module's external interface.
3. Remote but owned (Ports & Adapters)
Your own services across a network boundary (microservices, internal APIs). Define a port (interface) at the seam. The deep module owns the logic; the transport is injected as an adapter. Tests use an in-memory adapter. Production uses an HTTP/gRPC/queue adapter.
Recommendation shape: "Define a port at the seam, implement an HTTP adapter for production and an in-memory adapter for testing, so the logic sits in one deep module even though it's deployed across a network."
4. True external (Mock)
Third-party services (Stripe, Twilio, etc.) you don't control. The deepened module takes the external dependency as an injected port; tests provide a mock adapter.
Seam discipline
- One adapter means a hypothetical seam. Two adapters means a real one. Don't introduce a port unless at least two adapters are justified (typically production + test). A single-adapter seam is just indirection.
- Internal seams vs external seams. A deep module can have internal seams (private to its implementation, used by its own tests) as well as the external seam at its interface. Don't expose internal seams through the interface just because tests use them.
Testing strategy: replace, don't layer
- Old unit tests on shallow modules become waste once tests at the deepened module's interface exist — delete them.
- Write new tests at the deepened module's interface. The interface is the test surface.
- Tests assert on observable outcomes through the interface, not internal state.
- Tests should survive internal refactors — they describe behaviour, not implementation. If a test has to change when the implementation changes, it's testing past the interface.