The authoritative instructions are the repository-local testing-patterns skill. Repository guidance contains verified commands, behavior owners, fixture isolation, cleanup and examples.
Codex discovers .agents/skills/testing-patterns/SKILL.md and accepts
$testing-patterns. Claude Code discovers the relative directory symlink at
.claude/skills/testing-patterns and accepts /testing-patterns. Both use one body;
no plugin, global installation or host-specific frontmatter is required.
Validation evidence records client discovery, representative decisions and the limits of those checks.
The skill is adapted from the supplied 2026 research, preserving its qualifications: meaningful contracts and deliberate baselines, proportional failure evidence, legitimate doubles/structural checks, complementary test levels, and no universal test or mutation quota. Source identifiers and hashes are in the reference.
Historical evidence remains in the test-quality audit and deeper verification report. These describe completed work and its limits; they do not require repeating that work for each edit.