twisted.internet.testing.waitUntilAllDisconnected(reactor, protocols) function documentation

Take a list of disconnecting protocols, callback a Deferred when they're all done.

This is a hack to make some older tests less flaky, as ITransport.loseConnection is not atomic on all reactors (for example, the CoreFoundation, which sometimes takes a reactor turn for CFSocket to realise). New tests should either not use real sockets in testing, or take the advice in https://jml.io/pages/how-to-disconnect-in-twisted-really.html to heart.