# Test Gap from Diff

> Given a code diff, identify exactly which tests are missing — map changed functions to required test types using the test requirement matrix

- Skill: `diegosouzapw/test-gap-from-diff` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add diegosouzapw/test-gap-from-diff`
- Raw SKILL.md: https://api.skillmd.com/api/skills/diegosouzapw/test-gap-from-diff/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Security
- Author: diegosouzapw (https://skillmd.com/u/diegosouzapw)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/diegosouzapw/test-gap-from-diff

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# Test Gap from Diff Skill

Analyze a code diff to identify exactly which tests need to be written, using the test requirement matrix (rule 123) to determine required test types.

## Trigger Conditions
- Source code changes without corresponding test changes
- PR is created for review
- Coverage drops below threshold
- User invokes with "test gaps" or "test-gap-from-diff"

## Input Contract
- **Required:** Git diff or list of changed files
- **Optional:** Current coverage report

## Output Contract
- Per-function list of missing tests with required test type
- Priority ranking (critical path functions first)
- Test skeleton code for top-priority gaps
- Coverage delta estimate if tests are added

## Tool Permissions
- **Read:** Source files, test files, coverage reports
- **Write:** None (analysis only; test-engineer writes the tests)
- **Search:** Grep for function signatures, test file patterns

## Execution Steps

1. **Parse diff**: Extract list of changed functions/methods with file paths
2. **Classify changes**: Categorize each change per rule 123 matrix (model, service, handler, etc.)
3. **Determine required tests**: Map each change type to required test types (unit, integration, property, concurrency, fuzz)
4. **Check existing coverage**: For each changed function, check if required test types already exist
5. **Identify gaps**: List functions where required tests are missing
6. **Prioritize**: Rank gaps by: financial operations first, then public API, then internal logic
7. **Report**: Produce gap report with test type, priority, and estimated effort

## Success Criteria
- All changed functions mapped to required test types
- All existing test coverage identified
- Clear gap report with actionable items

## References
- `.cursor/rules/123-test-requirement-matrix.mdc`