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.cursor/rules/testing.mdc

Cursor testing rule for Rails

A Cursor `.mdc` rule can attach only when you touch tests. This variant keeps testing policy out of the always-on project rule so day-to-day edits stay quieter. This copy is written for a Rails project. This repository is a Ruby on Rails app. Follow the conventions already in the repo: MVC, migrations, and strong parameters. Do not introduce a second frontend stack.

The example uses a balanced, readable style, pragmatic tests, and comments only where the intent is not obvious. Open the generator to make the agent stricter, switch to test-first, quiet the comments, or pick a different file.

The example assumes a Rails app that uses migrations and Active Record. It does not assume Hotwire, React, or a particular auth gem. If the repo has chosen one, stay with it.

Customize in the generatorBrowse the library

Example file

Balanced strictness, readable style, pragmatic tests. Download name: testing.mdc

---
description: "Testing rules for a Rails repository"
globs: "**/test_*.rb"
alwaysApply: false
---

# Testing rules

Attach these rules when editing tests in this Rails repository.
The always-on project rule still lives in `.cursor/rules/project.mdc`. This file does not repeat it.

## Stack

This repository is a Ruby on Rails app. Follow the conventions already in the repo: MVC, migrations, and strong parameters. Do not introduce a second frontend stack.

## Commands

- Dev server: `bin/rails server`
- Tests: `bin/rails test`
- Migrate: `bin/rails db:migrate`

Use the script the repo already defines when it differs from the command above.

## Testing

Add or update tests when behavior changes.

Add a model or request test for the behavior you changed. Cover the forbidden parameter case.

## Done when

- The requested behavior works.
- `bin/rails test` passes, and `db:migrate` applies cleanly when the schema changed.
- The diff stays inside the task.
- You list anything you could not run.

Add it to the project

  1. 01

    Copy a starting file

    Copy the example Cursor testing rule on this page, or open the generator if you want different testing, strictness, or comment rules.

  2. 02

    Save it at .cursor/rules/testing.mdc

    Save it at `.cursor/rules/testing.mdc` in the Rails repo, next to the always-on project rule. Leave `alwaysApply` false so it only joins test edits.

  3. 03

    Start a fresh agent session

    Rules files are read when a session starts. A chat that is already open may still be using the old instructions.

  4. 04

    Give it one small task

    Ask for one change a Rails agent often gets wrong, such as a controller action that permits only the intended parameters. If it ignores the file, confirm the path and start a new session.

Questions about this file

Where do I put Cursor testing rule in a Rails repo?

Save it at `.cursor/rules/testing.mdc` in the Rails repo, next to the always-on project rule. Leave `alwaysApply` false so it only joins test edits.

Which tools read this Cursor testing rule?

Cursor loads `.cursor/rules/testing.mdc` when a file matches its globs. It does not replace `project.mdc`. Keep the always-on rule for stack conventions.

What does the Rails example assume?

The example assumes a Rails app that uses migrations and Active Record. It does not assume Hotwire, React, or a particular auth gem. If the repo has chosen one, stay with it.

Does VibeSpell upload my repository?

No. Recipe pages are static, and the generator builds the file in your browser from the options you pick. Your source code never leaves the machine.

Other files for Rails

Cursor testing rule for other stacks