From https://once.com/writebook

test/channels/application_cable/connection_test.rb

@@ -0,0 +1,19 @@
+require "test_helper"
+
+module ApplicationCable
+  class ConnectionTest < ActionCable::Connection::TestCase
+    test "connects with cookies" do
+      users(:kevin).sessions.start!(user_agent: "test", ip_address: "10.0.0.1").tap do |session|
+        cookies.signed[:session_token] = session.token
+      end
+
+      connect
+
+      assert_equal users(:kevin), connection.current_user
+    end
+
+    test "rejects connection without cookies" do
+      assert_reject_connection { connect }
+    end
+  end
+end