`push` times out from `handle_call`

[kybishop]

This only appears to be an issue from within a handle_call, possibly only within tests, but any call to push times out.

See this diff for a repro and note how the handle_call is executed (via the debug message) but then hangs on the push: https://github.com/NFIBrokerage/slipstream/compare/main...kybishop:ky/handle_call-timeout-example?expand=1, which causes it to fail the test on line 180

In handle_call for push


  1) test given the client is connected and joined to a topic we may assert_push/5 a push from the client via call/2, then reply/2 (Slipstream.SocketTestTest)
     test/slipstream/socket_test_test.exs:174
     ** (exit) exited in: GenServer.call(Slipstream.TestModeClient, {:push, "rooms:lobby", "msg:new", %{"foo" => "bar"}}, 5000)
         ** (EXIT) time out
     code: GenServer.call(@fixture, {:push, topic, event, params})
     stacktrace:
       (elixir 1.17.3) lib/gen_server.ex:1128: GenServer.call/3
       test/slipstream/socket_test_test.exs:180: (test)

[the-mikedavis]

This looks like a kind of a deadlock to me: the test process synchronously calls Slipstream.TestModeClient and in test mode, a Slipstream.push is a GenServer call to the test process. Because the test process is blocking waiting for the reply to its call it can't respond (via assert_push). As a workaround you can spawn a process to do the push:

spawn(fn -> GenServer.call(@fixture, {:push, topic, event, params}) end)

I'm not sure this can be fixed per se but it could be documented. (Maybe in assert_push?)