# Run the Test Suite and Triage Failures in Fastify with Atlas in 2026

> Atlas empowers Fastify developers to transform overwhelming `node:test` output into a clear, prioritized list of distinct root causes for efficient debugging.

Atlas helps Fastify developers in 2026 turn a wall of red `node:test` output into a prioritized list of distinct root causes by running the suite with its `bash` tool, capturing the complete log, and then using `grep` to group failures before recording them with `todowrite` for systematic resolution.

## Key takeaways

- Atlas `bash` captures the entire `node:test` output for Fastify, preventing truncation.
- Use `atlas grep` to identify distinct root causes in Fastify test logs, not just test names.
- Atlas `todowrite` helps track and prioritize Fastify fixes systematically.
- Iterative fixing with `atlas edit` and targeted `node --test` runs speeds up Fastify debugging.
- Atlas provides full transparency and approval for all Fastify code changes, including `prettier` formatting.

## How to Run Fastify Tests and Capture Full Output with Atlas

To run your Fastify test suite with Atlas, you use the `bash` tool, which ensures even long `node:test` outputs are fully captured. In 2026, Fastify developers rely on Atlas to manage the extensive output from `npm test` commands, preventing truncation of critical failure details, especially when dealing with 2000+ lines of logs.

When working with a Fastify application, running the full test suite often generates a significant volume of output from `node:test` and `fastify.inject()` calls. Atlas's `bash` tool is designed to execute your `npm test` command while guaranteeing that the entire log, regardless of its length, is retained. This is crucial because standard terminal buffers or even some AI model context windows might truncate output at around 2000 lines or 50 KB. By executing `atlas bash "npm test -- --timeout=60000"`, Atlas runs your `package.json` test script, which typically invokes `node --test` on files like `test/routes.test.js` or `test/plugins.test.js`. If the output exceeds the display limit, Atlas automatically writes the complete log to a temporary file and provides its path, ensuring no diagnostic information is lost.

## Analyzing Truncated Fastify Test Logs with Atlas

If your Fastify test output is truncated, Atlas provides a direct path to the complete log file, ensuring you never miss critical details. This feature is vital for debugging complex Fastify plugin interactions or JSON schema validation errors, where a single line of context can make a 100% difference in diagnosis.

After running a Fastify test suite with `atlas bash`, if the terminal output indicates truncation (e.g., '...output truncated...'), Atlas will explicitly tell you the path to the full log file. Instead of guessing or re-running tests, you can immediately access the complete `node:test` output. Use the `atlas read` tool to view this file directly within your terminal, for example, `atlas read /tmp/atlas-log-12345.txt`. This allows you to review every assertion failure from `fastify.inject()` calls, every stack trace, and every detail of your Fastify application's behavior, including specific plugin encapsulation contexts or decorator issues, without relying on a potentially incomplete view.

## Grouping Fastify Test Failures by Root Cause with Atlas `grep`

To efficiently triage Fastify test failures, Atlas's `grep` tool helps group distinct root causes from the complete log, rather than just by test name. This approach is far more effective than manually sifting through hundreds of lines of `node:test` output, especially when 10 or more tests might fail due to a single underlying issue.

Once you have the complete `node:test` log for your Fastify application, the next step is to identify distinct root causes. Simply grouping by test name can be misleading, as many tests might fail for the same reason (e.g., a broken database connection, an incorrect JSON schema, or a misconfigured plugin). Atlas's `grep` tool allows you to search the saved log file for common error patterns, stack trace origins, or specific Fastify error messages. For instance, you might `atlas grep "Error: EADDRINUSE" /tmp/atlas-log-12345.txt` to find port conflicts, or `atlas grep "Validation Error: data.body should be object"` to pinpoint schema issues. This method helps you consolidate multiple failures into a single, actionable root cause, making your triage process significantly more efficient.

## Tracking Fastify Fixes with Atlas `todowrite`

After identifying distinct root causes for Fastify test failures, Atlas's `todowrite` tool helps you create a prioritized list of fixes, ensuring no issue is forgotten. This structured approach prevents re-triage and keeps your focus on resolving the 1-2 most impactful problems first, rather than getting lost in a sea of individual test failures.

With distinct root causes identified from your `node:test` log, use `atlas todowrite` to create actionable tasks. Each `todowrite` entry should correspond to a single, distinct root cause, not individual failing tests. For example, instead of 'Fix `user-auth.test.js` failure', you might write 'Fix incorrect JWT token generation in `plugins/auth.js`' or 'Update `schemas/user.json` to allow optional email field'. Assigning a 'pending' status to these entries helps track progress. This ensures that when you fix one root cause, you address all related test failures across your Fastify application, whether they originate from `app.js`, a specific plugin, or a route handler using `fastify.inject()`.

## Iterative Fixing of Fastify Tests with Atlas `edit`

Atlas's `edit` tool facilitates an iterative fix-and-retest cycle for Fastify applications, allowing you to focus on one root cause at a time. This targeted approach, combined with re-running only affected `node:test` files, significantly reduces the feedback loop from 10+ minutes for a full suite to just seconds for a single test file.

Once you have a `todowrite` entry for a distinct Fastify test failure, use `atlas edit` to make the necessary code changes. For instance, if the issue is in `plugins/database.js`, you would `atlas edit plugins/database.js`. After making your changes, instead of running the entire `npm test` suite, you can use `atlas bash` to execute only the affected `node:test` files. For example, `atlas bash "node --test test/database.test.js"`. This rapid feedback loop is invaluable for Fastify development, where changes in one plugin can have cascading effects. Atlas also computes a unified diff for every file edit and surfaces it for approval, ensuring you review changes before they are written, and can even run `prettier` on touched plugins after approval.

## Atlas Safety and Review for Fastify Code Changes

Atlas integrates robust safety and review mechanisms into the Fastify development workflow, ensuring every code change is transparent and approved. From permission-gated tool calls to unified diffs for every edit, Atlas provides 100% control over modifications to your `app.js`, plugin files, or JSON schemas.

Atlas is designed with developer control at its core. Every tool call, including `bash`, `read`, `grep`, `todowrite`, and `edit`, is permission-gated against allow, ask, and deny rules before it runs. When Atlas drafts a plan to modify your Fastify codebase, it first presents it in a read-only plan agent and asks for your approval before switching to a build agent. For any file edit, such as changes to `app.js`, `plugins/auth.js`, or a `schemas/route.json` file, Atlas computes a unified diff and surfaces it for your approval before writing. This allows you to review exactly what changes Atlas proposes, ensuring that modifications to your Fastify application's plugin encapsulation, decorators, or JSON schemas are intentional and correct. Atlas can also snapshot file changes as git patches, allowing for easy diffing and rollback.

## Steps

1. Run the full Fastify test suite with Atlas `bash`, ensuring complete log capture: `atlas bash "npm test -- --timeout=60000"`
2. If output is truncated, use `atlas read` to view the complete `node:test` log file path provided by Atlas, e.g., `atlas read /tmp/atlas-log-12345.txt`.
3. Group Fastify test failures by distinct root cause using Atlas `grep` on the saved log, looking for patterns like 'Validation Error' or specific stack trace origins from `fastify.inject()` calls.
4. Record one `todowrite` entry per distinct root cause, with status 'pending', e.g., `atlas todowrite "Fix missing JSON schema for POST /users in app.js"`.
5. Select a `todowrite` entry and use `atlas edit` to modify the relevant Fastify file, such as `schemas/user.json` or `plugins/auth.js`.
6. After editing, re-run only the affected `node:test` files using `atlas bash`, e.g., `atlas bash "node --test test/user.test.js"`.
7. Approve the diff presented by Atlas for the file changes, then let Atlas run `prettier` on the touched Fastify plugins or route files.

## FAQ

### How does Atlas handle large Fastify `node:test` outputs?

Atlas's `bash` tool executes your `npm test` command and ensures the complete `node:test` output, regardless of its size (even over 2000 lines or 50 KB), is captured. If the output is too large for the terminal, Atlas writes it to a temporary file and provides the path, which you can then view with `atlas read`.

### Can Atlas help me find the root cause of Fastify plugin failures?

Yes, after capturing the full `node:test` log, you can use `atlas grep` to search for specific error messages, stack traces, or Fastify-related keywords within the log. This helps you pinpoint the underlying issue in your plugin encapsulation contexts or decorator implementations, rather than just seeing a failing test name.

### How does Atlas ensure I review changes to my Fastify application?

Atlas provides a unified diff for every file edit it proposes, whether it's to `app.js`, a Fastify plugin, or a JSON schema. This diff is surfaced for your approval before any changes are written to disk. Atlas also drafts a plan in a read-only agent and asks for permission before executing any build steps.

### Does Atlas integrate with Fastify's `prettier` formatter?

Yes, after you approve a code change made by Atlas to your Fastify application, Atlas can automatically run `prettier` on the touched plugins or route files. This ensures your codebase maintains consistent formatting according to your `prettier` configuration.

### How do I re-run only specific Fastify tests after a fix?

After using `atlas edit` to implement a fix, you can use `atlas bash` to execute only the relevant `node:test` files. For example, if you fixed an issue in `plugins/users.js`, you might run `atlas bash "node --test test/users.test.js"` to quickly verify your changes without running the entire suite.

### Can Atlas help track multiple Fastify bugs at once?

Absolutely. After grouping failures by distinct root causes using `grep`, you can use `atlas todowrite` to create a prioritized list of tasks. Each entry represents a unique problem in your Fastify application, allowing you to track and resolve them systematically, one at a time, without losing sight of other pending issues.

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