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.cursor/rules/testing.mdc

Cursor testing rule for LangChain

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 LangChain project. This repository builds LLM agents or chains. Model names and prompts are explicit. Tool calls validate their arguments. API keys stay in the environment.

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 Python agent stack such as LangChain or a similar orchestrator already in the repo. It does not assume LangGraph versus a simple chain, or a hosted tracer. Use what the project already imports.

Customize in the generatorBrowse the library

Example file

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

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

# Testing rules

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

## Stack

This repository builds LLM agents or chains. Model names and prompts are explicit. Tool calls validate their arguments. API keys stay in the environment.

## Commands

- Tests: `pytest`
- Lint: `ruff check .`
- Eval: `Run the project's eval script if it has one`

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

## Testing

Add or update tests when behavior changes.

Test the tool with a fake model or a direct function call. Assert the side effect did not run on invalid input.

## Done when

- The requested behavior works.
- `pytest` passes, including a test that a bad tool argument does not reach the side effect.
- 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 LangChain 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 LangChain agent often gets wrong, such as a tool whose arguments are validated before it touches the filesystem or the network. 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 LangChain repo?

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

The example assumes a Python agent stack such as LangChain or a similar orchestrator already in the repo. It does not assume LangGraph versus a simple chain, or a hosted tracer. Use what the project already imports.

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 LangChain

Cursor testing rule for other stacks