I can test this by restarting a websocket-relay container in the middle of a session.

I don't know how to automatically test this, as the WebSocket needs to be killed. Merely calling close on the socket would be considered a clean close.

Perhaps it could be done with Toxiproxy: https://github.com/Shopify/toxiproxy#down

@dentarg Using Toxiproxy is a nice idea, but I ran into a couple issues.

• The browser tests run entirely from the browser, and toxiproxy-node-client uses Node.js native methods, so that didn't work.
• When I created a simple client in-test (copying from an existing branch), I was stopped by the lack of Access-Control-Allow-Origin headers.
• Getting pass that, I would get blocked again because the Toxiproxy specifically blocks browsers from the API.
• I don't see any obvious escape hatch in the implementation of @vitest/browser to run code on the Node.js side.

Saying all that, there is still playwright and a web app could be spun up, "clicked" through, and then shut down, but that would require even more files and setup. Or someone could take on creating and hosting a custom build of Toxiproxy.

I'm happy with just manually testing part of this change.

The branch with toxiproxy is here if anyone would like to play more with it: https://github.com/ngbrown-forks/amqp-client.js/tree/error-on-websocket-close-toxiproxy

@ngbrown Thanks for trying, I don't see a way either, not until vitest-dev/vitest#3758 has landed so we can use https://playwright.dev/docs/emulation#user-agent from vitest. Looks like it is possible to make requests with mode no-cors (picked that up from https://hackerone.com/reports/236349 linked in Shopify/toxiproxy#219). Oh well :)

Is there anything else that needs done for this pull request?