Test-Driven Development

Project Context

• git installed: !which git 2>/dev/null || echo "not installed"
• current branch: !git branch --show-current 2>/dev/null || echo unknown
• CLAUDE.md: !find . -maxdepth 1 -name "CLAUDE.md" -type f
• project-discovery.md: !find . -maxdepth 3 -name "project-discovery.md" -type f
• personal config directory: !bash "${CLAUDE_PLUGIN_ROOT}/scripts/han-config-dir.sh" 2>/dev/null || echo "$HOME/.claude"
• project .han/config.md: !cat .han/config.md 2>/dev/null || echo ""

As your first action, use the Read tool on .han/config.md inside the personal config directory path above. A read that returns no file is no personal configuration: continue silently. When that file or the project .han/config.md probe supplies content, apply it per config-rule.md, which governs precedence between the two files, relative-path resolution, and what to do with a file that reads but cannot be used.

Constraints (read before anything else)

This skill writes production and test code in your working tree. It is an execution skill, not a document generator. These constraints shape every step and override any instinct to move faster.

• The observed-failure gate is load-bearing. No production-code change until a test has been run and observed to fail for the intended reason in this loop. A test that passes on first run is a stop-and-diagnose signal, not progress. This single rule is what separates real TDD from TDD-flavored code. The verbatim Three Laws and Canon TDD steps it derives from are in references/tdd-loop.md; pull that reference when a step needs the canon or the implementation gears.
• The scope gate is the observed-failure gate's companion. The observed-failure gate proves a red is genuine. It does not prove the test deserved to exist in this build. No production-code change outside the scope boundary recorded in Step 1, and least of all in shared or cross-application code other consumers depend on. A list item whose green requires an out-of-scope edit is a stop, never an implement; Step 2 carries the resolution ladder that Step 3 works.
• Two hats. Never refactor while any test is red. See references/tdd-loop.md for the canonical statement.
• One behavior at a time. Exactly one test list item becomes one runnable test per loop. Newly discovered scenarios are written to the list and deferred, never implemented in the current loop.
• BDD framing. Tests describe observable behavior, named in the project's existing test-naming convention, asserting outcomes through the public interface — never private state. The behavior-naming and Given/When/Then protocol is in references/bdd-framing.md; pull it when Step 2 needs it.
• You will be tempted to fake this. The specific ways an agent fakes TDD, and the discipline that catches each, are in references/failure-modes.md; pull it when a loop feels off (a test passes on first run, no red is shown, the implementation has outrun the test, refactor is being skipped).
• YAGNI governs the refactor step and the test list. Apply the rule in ../../references/yagni-rule.md: remove duplication, but do not add abstractions,