rpsec matcher for matching ActiveSupport::Notifications events

active_support_notification_matcher.rb

# usage: 
# expect {}.to publish_notification("object:created").with({:id => 1})
# expect {}.to publish_notification("object:created").with {|actual_payload| actual_payload[:id].present? }
module ActiveSupportNotificationMatchers
  class PublishNotifications

    def initialize(event_name)
      @event_name = event_name
      @payload    = nil
    end

    def with(payload=nil,&block)
      @payload = payload || block
      self
    end

    def matches?(given_proc)
      @verifier = MessageVerifier.new(@event_name, @payload)
      ActiveSupport::Notifications.subscribe(@event_name, @verifier)
      given_proc.call
      @verifier.satisfied?
    end

    def failure_message
      msg = "Expected event '#{@event_name}' with #{@payload.inspect} as payload to get published. "
      if @verifier.actual_event_name
        msg << "got event '#{@verifier.actual_event_name}' with #{@verifier.actual_payload} as payload."
      else
        msg << "no message received."
      end
    end

    def description
      "Expect #{@event_name} to get published with payload #{@payload.inspect}"
    end
  end
  
  class MessageVerifier
    attr_accessor :actual_event_name, :actual_payload, :expected_event_name, :expected_payload

    def initialize(event_name, payload)
      @expected_event_name = event_name
      @expected_payload = payload
    end

    def call(event_name, payload)
      @actual_event_name = event_name
      @actual_payload = payload
    end

    def payload_satisfied?
      return true unless @expected_payload
      if @expected_payload.respond_to?(:call)
        return @expected_payload.call(@actual_payload)
      else
        @expected_payload == @actual_payload
      end
    end

    def event_name_satisfied?
      @expected_event_name == @actual_event_name
    end

    def satisfied?
      payload_satisfied? && event_name_satisfied?
    end
  end

  def publish_notification(event_name)
    PublishNotifications.new(event_name)
  end
end