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.cursor/rules/testing.mdc

Cursor testing rule for FastAPI

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 FastAPI project. This repository is a FastAPI service. Request and response bodies are Pydantic v2 models. Routes stay async and must not block the event loop.

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 FastAPI with Pydantic v2 and pytest. It does not assume a specific database. If the project uses SQLAlchemy, Tortoise, or raw SQL, keep that choice.

Customize in the generatorBrowse the library

Example file

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

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

# Testing rules

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

## Stack

This repository is a FastAPI service. Request and response bodies are Pydantic v2 models. Routes stay async and must not block the event loop.

## Commands

- Dev server: `uvicorn app.main:app --reload`
- Tests: `pytest`
- Lint: `ruff check .`
- Format: `ruff format .`

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

## Testing

Add or update tests when behavior changes.

Test the route with the project's HTTP client (httpx or TestClient). Cover the success path and one rejection.

## Done when

- The requested behavior works.
- `pytest` passes and `ruff check .` is clean, or you say which tool the repo does not have.
- 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 FastAPI 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 FastAPI agent often gets wrong, such as a route that rejects a bad payload with a 422 instead of trusting the dict. 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 FastAPI repo?

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

The example assumes FastAPI with Pydantic v2 and pytest. It does not assume a specific database. If the project uses SQLAlchemy, Tortoise, or raw SQL, keep that choice.

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 FastAPI

Cursor testing rule for other stacks