# Testing Wallaby > Debug and fix failing tests using Wallaby.js MCP tools. Use when investigating test failures, debugging test errors, inspecting runtime values, checking code coverage, or updating snapshots. Use when this capability is needed. - Skill: `tomevault-io/testing-wallaby` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/testing-wallaby` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/testing-wallaby/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/testing-wallaby --- # Testing with Wallaby Use Wallaby MCP tools as the primary way to work with tests. Fall back to terminal only if Wallaby is unavailable. ## Debug Workflow ### 1. Identify failures - **Broad**: `wallaby_failingTests` — all failing tests in the project - **By file**: `wallaby_failingTestsForFile` — failures related to a specific source or test file - **By line**: `wallaby_failingTestsForFileAndLine` — failures covering a specific line Each returns test name, test ID, errors with stack traces, runtime logs, and coverage percentage. ### 2. Narrow down with coverage - `wallaby_coveredLinesForFile` — which lines a file has covered, optionally filtered by test ID - `wallaby_coveredLinesForTest` — all files/lines a specific test covers Use coverage to find the implementation code a failing test actually executes. ### 3. Inspect runtime values - `wallaby_runtimeValues` — value of an expression at a file/line across all tests - `wallaby_runtimeValuesByTest` — value of an expression at a file/line for a specific test Required params: `file`, `line` (1-based, count blank lines), `lineContent`, `expression`. For `runtimeValuesByTest`, also `testId`. ### 4. Fix the code Apply the fix based on evidence from steps 1-3. ### 5. Verify the fix - `wallaby_testById` — re-check a specific test by its ID - `wallaby_failingTests` — confirm no remaining failures Iterate steps 3-5 until the test passes. ### 6. Update snapshots (if needed) - `wallaby_updateTestSnapshots` — update snapshots for one test (by test ID) - `wallaby_updateFileSnapshots` — update all snapshots in/covering a file - `wallaby_updateProjectSnapshots` — update every snapshot in the project ## Discovery Tools Use these when exploring tests, not just debugging failures: - `wallaby_allTests` — list every test in the project - `wallaby_allTestsForFile` — tests related to a specific file - `wallaby_allTestsForFileAndLine` — tests covering a specific file and line ## Principles - Always cite runtime values and coverage data to justify conclusions. - Explain reasoning step by step. - Keep iterating with updated Wallaby data until the test passes. --- > Source: [DZakh/sury](https://github.com/DZakh/sury) — distributed by [TomeVault](https://tomevault.io).