Pytest MCP Server

A Model Context Protocol (MCP) server that enables AI assistants like Claude to run and analyze pytest tests for desktop applications.

Overview

This project demonstrates how to integrate pytest with AI assistants through MCP. It includes:

• Real Desktop Application: A fully functional calculator app built with tkinter

• Comprehensive Test Suite: pytest tests covering UI, functionality, and edge cases

• MCP Server: Connects pytest to AI assistants for interactive testing

Related MCP server: Debug Companion MCP

Project Structure

pytest-mcp-server/
├── src/
│   ├── __init__.py
│   └── calculator_app.py      # Desktop calculator application
├── tests/
│   ├── __init__.py
│   └── test_calculator.py     # Pytest test suite
├── server.py                   # MCP server implementation
├── pyproject.toml             # Project configuration
└── README.md

Installation

Prerequisites

• Python 3.10 or higher

• pip package manager

Setup

1. Clone or navigate to the project directory:

cd /Users/303748/Documents/ws/pytest-mcp-server

2. Create a virtual environment:

python3 -m venv venv
source venv/bin/activate  # On Windows: venv\Scripts\activate

3. Install dependencies:

pip install -e .

Or install with development dependencies:

pip install -e ".[dev]"

Running the Calculator App

To run the desktop calculator application:

python -m src.calculator_app

Or use the installed script:

calculator-app

Running Tests Manually

Run all tests:

pytest tests/

Run with verbose output:

pytest tests/ -v

Run only UI tests:

pytest tests/ -m ui

Run tests excluding slow ones:

pytest tests/ -m "not slow"

Run specific test class:

pytest tests/test_calculator.py::TestBasicOperations

Using the MCP Server

Configuration

1. Find your Claude Desktop config file:

   • macOS: ~/Library/Application Support/Claude/claude_desktop_config.json

   • Windows: %APPDATA%\Claude\claude_desktop_config.json

2. Add the MCP server configuration:

IMPORTANT NOTICE: You need to give execution rights to the run_server.sh file

{
  "mcpServers": {
    "pytest": {
      "command": "/Users/303748/Documents/ws/pytest-mcp-server/run_server.sh",
      "args": []
    }
  }
}

3. Restart Claude Desktop

Using with Claude

Once configured, you can interact with your tests through Claude:

Example conversations:

You: "List all available tests in the calculator project"

You: "Run the UI tests for the calculator"

You: "Run only the error handling tests"

You: "Show me the results of the last test run"

You: "The addition test is failing, can you help me debug it?"

MCP Server Tools

The server provides three main tools:

1. run_tests

Executes pytest tests with specified options.

Parameters:

• test_path (required): Path to test file or directory

• markers (optional): Pytest markers to filter tests

• verbose (optional): Show detailed output (default: true)

• capture (optional): Output capture method (default: "no")

2. list_tests

Lists all available tests without running them.

Parameters:

• test_path (optional): Path to scan for tests (default: "tests/")

3. get_test_results

Retrieves and formats the last test run results.

Parameters: None

Test Markers

The test suite uses these markers:

• @pytest.mark.ui - UI-related tests

• @pytest.mark.error_handling - Error handling tests

• @pytest.mark.slow - Slow-running tests

Development

Running Tests with Coverage

pytest tests/ --cov=src --cov-report=html

View coverage report:

open htmlcov/index.html  # macOS

Code Formatting

Format code with Black:

black src/ tests/ server.py

Lint code with Ruff:

ruff check src/ tests/ server.py

Calculator Features

The calculator application supports:

• Basic operations: Addition, subtraction, multiplication, division

• Advanced operations: Square root

• UI controls: Clear (C), Clear Entry (CE), Backspace (←)

• Decimal numbers: Full decimal support

• Error handling: Division by zero, negative square roots, invalid expressions

Test Coverage

The test suite includes:

Basic Operations

• Addition

• Subtraction

• Multiplication

• Division

• Division by zero handling

Advanced Operations

• Square root calculations

• Square root of negative numbers

• Decimal number operations

UI Functions

• Clear button functionality

• Clear entry functionality

• Backspace operation

• Chaining multiple operations

Edge Cases

• Very large numbers

• Operations with zero

• Invalid expressions

Troubleshooting

Tests not running

Make sure you're in the project directory and have activated the virtual environment:

cd /Users/303748/Documents/ws/pytest-mcp-server
source venv/bin/activate
pytest tests/

MCP server not connecting

1. Check that the path in claude_desktop_config.json is correct

2. Ensure Python is in your PATH

3. Restart Claude Desktop after configuration changes

4. Check Claude Desktop logs for error messages

Import errors

Make sure the package is installed in editable mode:

pip install -e .

Contributing

Contributions are welcome! Areas for improvement:

• Add more calculator features (memory, history)

• Implement screenshot capture on test failures

• Add performance benchmarking tools

• Create more test scenarios

• Improve error messages

Resources

• MCP Documentation

• Pytest Documentation

• Claude Desktop

Author

Created as an example project for the LinkedIn article "Building an MCP Server for Pytest: Automating Desktop Application Testing"