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How to Mock anyio.run Backends (asyncio vs trio) in Python

Demonstrates how to mock anyio.run to verify backend selection (asyncio or trio) without actually running the event loop.

anyio async testing

Python

import anyio
from unittest.mock import Mock, patch


async def fetch_data():
    await anyio.sleep(0.1)
    return {"data": 42}


def run_with_backend(backend: str):
    async def main():
        result = await fetch_data()
        print(f"[{backend}] Result: {result}")

    anyio.run(main, backend=backend)


if __nam…

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