tdd

TDD protects meaningful behavior. RED -> GREEN -> REFACTOR for domain rules, branches, state, validation, async effects, and integration contracts. Types, wiring, copy/styles, and behavior-preserving deletion may use focused verification. Coverage is never a target.

Test seams and anti-patterns

• Seams: test public boundaries. Name the seam first; confirm pre-agreed seams with the user when issue and convention leave it unclear. No tests at unconfirmed internals. Use /codebase-design rather than inventing a seam for convenience.
• Tautological tests: expected values need an independent source of truth: literal, worked example, fixture, spec, or observation.
• Source-text proxies: delete tests that scan implementation, CSS, markup, or config for tokens or regexes as runtime proof. Replace at a public seam when behavior matters; use static analysis for syntax. Keep content assertions for public output only.
• Vertical slices: use vertical slices: one RED test plus GREEN implementation at a time; bulk tests encode imagined behavior.

Workflow

Contract

• Name public behavior; follow the domain glossary and ADRs.
• Choose the smallest test that fails if it breaks. Add cases only for independent credible risks.
• For high-cardinality/state-sequence invariants, read PROPERTY-BASED-TESTING.md; require an independent oracle and replay.
• For long-lived browser resource lifetimes, use repeatable round trips and SOAK-TESTING.md; fresh contexts cannot reveal accumulation.
• Use /read-the-damn-docs for external contracts and tests.md when shape is unclear.