class MockQueue
  attr_reader :messages

  def initialize
    @messages = []
    @subscription_id = 0
    @subscriptions = {}
  end

  def subscribe(&block)
    @subscription_id += 1
    @subscriptions[@subscription_id] = block
    @subscription_id
  end

  def push(message)
    @messages.push(message)
    @subscriptions.values.each do |callback|
      callback.call(message)
    end
    message
  end

  def clear_messages!
    @messages = []
  end

  def unsubscribe(subscription_id)
    @subscriptions.delete(subscription_id)
    nil
  end
end