TempCluster() and pytest

• asyncpg version: 0.23.0
• PostgreSQL version: N/A
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: N/A
• Python version: 3.8.9 (but N/A)
• Platform: N/A
• Do you use pgbouncer?: N/A
• Did you install asyncpg with pip?: yes
• If you built asyncpg locally, which version of Cython did you use?:
• Can the issue be reproduced under both asyncio and
  uvloop?:

This is issue which happens when using TempCluster() for testing as mentioned in https://github.com/MagicStack/asyncpg/issues/589.

Basically invoking cluster.start() causes an error when trying to use in environment that sets up own event loop (like pytest). Because .start() calls self._test_connection(timeout=wait) which creates and uses own event loop (https://github.com/MagicStack/asyncpg/blob/d08a9b8b9c2c68d469aeb9c4112d83c56c24f11c/asyncpg/cluster.py#L467).

This can be worked around by using nest_asyncio package, but it would be great if we could pass the event loop to the start() method so no hacking around that would be needed.

Il problema segnalato si trova in asyncpg/cluster.py, nella parte relativa a TempCluster.start() e alla relativa chiamata a _test_connection(timeout=wait). Riproduci il percorso di avvio con pytest o in un altro ambiente con un proprio event loop, quindi determina come dovrebbe propagarsi lungo tale percorso l'argomento loop richiesto. Il lavoro è completato quando cluster.start() può usare l'event loop del chiamante senza richiedere nest_asyncio, con una coverage per lo scenario segnalato.