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.cursor/rules/testing.mdc

Cursor testing rule for T3

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 T3 project. This repository is a T3 app: Next.js, tRPC, and the database client the repo already uses. Inputs are validated with Zod. The database is never imported into a client component.

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 T3-style Next.js app with tRPC. It does not assume Prisma versus Drizzle, or a particular auth library. Use the one in the repo.

Customize in the generatorBrowse the library

Example file

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

---
description: "Testing rules for a T3 repository"
globs: "**/*.{test,spec}.ts"
alwaysApply: false
---

# Testing rules

Attach these rules when editing tests in this T3 repository.
The always-on project rule still lives in `.cursor/rules/project.mdc`. This file does not repeat it.

## Stack

This repository is a T3 app: Next.js, tRPC, and the database client the repo already uses. Inputs are validated with Zod. The database is never imported into a client component.

## Commands

- Dev server: `npm run dev`
- Typecheck: `npm run typecheck`
- Tests: `npm test`

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

## Testing

Add or update tests when behavior changes.

Call the procedure with a caller or the project's test helper. Cover one invalid Zod input.

## Done when

- The requested behavior works.
- `npm run typecheck` passes and the procedure rejects an invalid input.
- 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 T3 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 T3 agent often gets wrong, such as a tRPC procedure that validates input with Zod and rejects a bad id. 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 T3 repo?

Save it at `.cursor/rules/testing.mdc` in the T3 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 T3 example assume?

The example assumes a T3-style Next.js app with tRPC. It does not assume Prisma versus Drizzle, or a particular auth library. Use the one in the repo.

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 T3

Cursor testing rule for other stacks