class RSpec::Rails::Matchers::ActionCable::HaveBroadcastedTo

def failure_message
  "expected to broadcast #{base_message}".tap do |msg|
    if @unmatching_msgs.any?
      msg << "\nBroadcasted messages to #{stream}:"
      @unmatching_msgs.each do |data|
        msg << "\n   #{data}"
      end
    end
  end
end