FastMCP Testing Demo

A comprehensive example demonstrating FastMCP testing patterns with pytest-asyncio.

Overview

This example shows how to:

• Set up pytest-asyncio configuration in pyproject.toml
• Write async test fixtures for MCP clients
• Test tools, resources, and prompts
• Use parametrized tests for multiple scenarios
• Leverage inline-snapshot and dirty-equals for assertions

Project Structure

testing_demo/
├── pyproject.toml          # Project config with pytest-asyncio setup
├── server.py               # Simple MCP server with tools/resources/prompts
├── tests/
│   └── test_server.py      # Comprehensive test suite
└── README.md               # This file

Key Features

pyproject.toml Configuration

The pyproject.toml includes the critical pytest-asyncio configuration:

[tool.pytest.ini_options]
asyncio_mode = "auto"

This eliminates the need for @pytest.mark.asyncio decorators on every async test.

Server Components

The demo server (server.py) includes:

• Tools: add, greet, async_multiply
• Resources: demo://info, demo://greeting/{name}
• Prompts: hello, explain

Test Patterns

The test suite demonstrates:

1. Async fixture pattern: Proper client fixture using async with
2. Tool testing: Calling tools and checking results via .data attribute
3. Resource testing: Reading static and templated resources
4. Prompt testing: Getting prompts with different arguments
5. Parametrized tests: Testing multiple scenarios efficiently
6. Schema validation: Verifying tool schemas and structure
7. Pattern matching: Using dirty-equals for flexible assertions

Running the Tests

# Install dependencies
uv sync

# Run all tests
uv run pytest

# Run with verbose output
uv run pytest -v

# Run a specific test
uv run pytest tests/test_server.py::test_add_tool

Running the Server

# Run the server
uv run fastmcp run server.py

# Inspect the server
uv run fastmcp inspect server.py

Learning More

For detailed information about testing FastMCP servers, see the Testing Documentation.