`subscribe_to` rSpec matcher for use with Wisper

subscribe_to.rb

RSpec::Matchers.define :subscribe_to do |event_name|
  match do |domain|
    @is_registered = Wisper::GlobalListeners.registrations.any? do |registration|
      if event_name == :any_event
        registration.on.send(:list).nil? &&
          (@asynchronously.blank? || registration.broadcaster.is_a?(Wisper::SidekiqBroadcaster))
      else
        registration.listener == domain &&
          registration.on.include?(event_name) &&
          (@asynchronously.blank? || registration.broadcaster.is_a?(Wisper::SidekiqBroadcaster))
      end
    end

    return true if @is_registered && event_name == :any_event

    if @is_registered
      expect(domain).to respond_to(event_name)

      handler_class = build_handler_class(event_name, domain)
      handler = instance_double(handler_class)

      expect(handler_class).to receive(:new).with(a: 10, b: 20) { handler }
      expect(handler).to receive(:call!)

      domain.public_send(event_name, a: 10, b: 20)
      true
    end
  end

  chain :asynchronously do
    @asynchronously = true
  end

  private

  def build_handler_class(event_name, domain)
    handler_name = event_name.to_s.sub('__', '/').classify
    handler_name += 'Handler'
    handler_name.remove!('::')
    handler_name = handler_name.prepend("#{domain.name}::")
    handler_name.constantize
  end
end