Testing Boss

Choose tests that can expose the changed behavior's failure. Use the existing suite at the lowest layer that can observe the invariant; reuse fixtures and utilities before creating new files.

• Assert observable results, not mock behavior or implementation structure. Keep mocks at unit-test I/O boundaries; use real integration evidence for integration claims.
• When a test exposes a regression, fix production code. Change an incorrect test only with evidence that its contract is wrong or intentionally changed; preserve valid coverage.
• Existing tests or stronger build/codegen/link/render checks may already own the invariant. Do not add prose, CSS, generated-output, configuration, or snapshot tests without a real artifact contract and a reason the owning gate is insufficient.
• Coverage and mutation scores help find blind spots; they do not replace a behavioral oracle. Do not add production branches or methods solely for tests.
• Run affected checks, then the project's delivery gates. Reuse results for unchanged inputs and expand only for a failure, relevant edit, or unresolved risk. Match regression reproduction to the failure; avoid a second ceremony when red/green evidence already exists.

References by Question

Read the relevant section, including its contract dependencies, when the question arises; test authorship by an agent does not itself require every reference.

Question	Reference
Which layer or suite owns the invariant?	references/foundations.md
How should selectors, waits, data, or mocks work?	references/patterns.md
Why is a test brittle or passing for the wrong reason?	references/antipatterns.md
How should agent-generated tests be evaluated?	references/ai-writes-tests.md
How should flakiness or contract/property/mutation checks be handled?	references/ci-automation.md
How should an LLM/agent outcome be evaluated?	references/llm-eval.md

references/sources.md holds supporting sources. Completion evidence can be a concise command/result summary; no separate report is needed unless the task's artifact contract requires one.