Code Testing Agent

Analyze code and suggest specific, purpose-driven tests tied to actual behavior. Strive to meet the project's coverage target, or maximize coverage when no target is defined.

Freedom level: Flexible — Follow these steps in order. Adapt depth to the code's complexity and the user's request.

When not to use

Does not run tests — use running-tests. Does not review code quality — use code-review-agent.

Table of Contents

• Step 0 — Create Progress Todos
• Step 1 — Identify Target Code
• Step 2 — Search for Implementation Plan
• Step 3 — Analyze the Code
• Step 4 — Detect Project Test Infrastructure
• Step 5 — Suggest Tests with Rationale
• Step 6 — Offer to Write Test Files

Step 0 — Create Progress Todos

Use TodoWrite to create todos for Steps 1–6 (all status: "pending"). Mark each status: "completed" as you finish.

Step 1 — Identify Target Code

Resolve the target code using this priority order. Load references/input-resolution.md for detailed parsing heuristics.

1. File path argument — parse the invocation message for a file path
2. Function/method argument — note any named function; scope Step 3 to it once a file is resolved
3. Pasted code — use the inline code block as an anonymous file
4. Conversation context — recently created, edited, or discussed file
5. Recent changes — git diff --name-only HEAD~1 (exclude test/config/lock files); confirm with user
6. Ask — "Which code would you like me to suggest tests for?"

Report: file(s) to analyze, function scope if any, full-file vs. scoped. Read each target file in full.

Step 2 — Search for Implementation Plan

Search for design intent (stop at first match):

1. User's message
2. docs/plans/ — match by filename similarity to target code
3. ~/.claude/plans/ — same matching logic
4. git log --oneline -5 — commit messages describing intent
5. Inline // TODO, // PLAN:, // PURPOSE:, or JSDoc @description in the target code

If found: report "Found plan: [path]. Using it to understand intended behavior." Extract goal, key behaviors, edge cases, and acceptance criteria.

If not found: report "No implementation plan found. Inferring intent from code and context." Proceed to Step 3.

Step 3 — Analyze the Code

Load references/test-analysis-guide.md for detailed heuristics. Analyze:

• 3a. Behavioral summary — 2–4 sentences on purpose and primary behavior
• 3b. Critical paths — happy path, error paths, branching logic, state transitions
• 3c. Integration points — external APIs, file system, events, internal modules, env config
• 3d. Implicit contracts — return shape, side effects, ordering, idempotency guarantees
• 3e. Fragility — complex conditionals, regex, math, null chains, index arithmetic

Step 4 — Detect Project Test Infrastructure

Load references/test-infrastructure.md for config file locations and glob patterns. Detect:

• 4a. Test framework — from package.json, pytest.ini, Cargo.toml, CI config, etc.
• 4b. Existing test files — glob for *.test.*, *.spec.*, *_test.* near the target
• 4c. Existing patterns — read 1–2 test files for import style, mocking, conventions
• 4d. Coverage target — from jest.config.*, pyproject.toml, .nycrc, codecov.yml

Report: "Detected: [framework]. Existing tests use [patterns]. Coverage target: [X]%."

Step 5 — Suggest Tests with Rationale

Load references/output-guide.md for the full output template and suggestion principles.

For each suggestion provide: What (behavior), Why (blast radius if missing), How (approach + key assertions), Where (file path). Group by file; prioritize by blast radius.

Step 6 — Offer to Write Test Files

Ask: "Would you like me to write the test file(s)? I will create [path(s)] with the tests above."

• Yes — write complete files using detected conventions (Priority 1 + 2; confirm before including Priority 3). Suggest [test command] to verify.
• No — "The suggestions above should give you a clear starting point."
• Partial — write only the requested subset.