Cabin mocking - it can be done

cabin_mocking.rb

    class LogTracker
      def cache()
        @cache ||= Hash.new{|h,k| h[k] = []}
      end

      def <<(hash)
        hash.each{|k,v| cache[k].push(v) }
      end
    end

    context "when using a Json string, tags might be an ArrayList" do
      let(:tcp) { double('tcpsocket') }
      let(:mocklog) { LogTracker.new }
      let(:tracker) do
        instance = Cabin::Channel.new
        instance.level = :debug
        instance.subscribe(mocklog)
        instance
      end

      it "#receive will fail unless the ArrayList implements compact" do
        allow(Cabin::Channel).to receive(:get).and_return(tracker)
        allow(TCPSocket).to receive(:new).and_return(tcp)
        allow(UDPSocket).to receive(:new).and_return(tcp)
        allow(tcp).to receive(:<<)
        allow(tcp).to receive(:read).with(4).and_return("\x00\x00\x00\x02")
        allow(tcp).to receive(:read).with(2).and_return("\x10\x01")

        json_string = '{"tags":["good_enough", "smart_enough", "doggone_it", "people_like_me", null], "message":"hello", "node_info":{"name":"node1", "status":"up"}, "@version":"1", "@timestamp":"2015-06-03T23:34:54.076Z", "host":"vagrant-ubuntu-trusty-64"}'
        event = LogStash::Event.new(LogStash::Json.load(json_string))
        output = LogStash::Plugin.lookup("output", "riemann").new
        expect {output.register}.not_to raise_error
        output.receive(event)
        expect(mocklog.cache[:error]).to eq([])
      end
    end

fail_console_output.txt

uy at Elastics-MacBook-Pro in ~/elastic/logstash-output-riemann on master*
$ be rspec ./spec/outputs/riemann_spec.rb:123
Using Accessor#strict_set for specs
Run options:
  include {:locations=>{"./spec/outputs/riemann_spec.rb"=>[123]}}
  exclude {:redis=>true, :socket=>true, :performance=>true, :couchdb=>true, :elasticsearch=>true, :elasticsearch_secure=>true, :export_cypher=>true, :integration=>true, :windows=>true}

outputs/riemann
  build_riemann_formatted_event
    when using a Json string, tags might be an ArrayList
      #receive will fail unless the ArrayList implements compact (FAILED - 1)

Failures:

  1) outputs/riemann build_riemann_formatted_event when using a Json string, tags might be an ArrayList #receive will fail unless the ArrayList implements compact
     Failure/Error: expect(mocklog.cache[:error]).to eq([])

       expected: []
            got: [#<NoMethodError: undefined method `compact' for #<Java::JavaUtil::ArrayList:0x8c11eee>>]

       (compared using ==)

       Diff:
       @@ -1,2 +1,2 @@
       -[]
       +[#<NoMethodError: undefined method `compact' for #<Java::JavaUtil::ArrayList:0x8c11eee>>]

     # ./spec/outputs/riemann_spec.rb:146:in `(root)'

Finished in 0.474 seconds (files took 0.52 seconds to load)
1 example, 1 failure

Failed examples:

rspec ./spec/outputs/riemann_spec.rb:133 # outputs/riemann build_riemann_formatted_event when using a Json string, tags might be an ArrayList #receive will fail unless the ArrayList implements compact

Randomized with seed 41588

good_console_output.txt

guy at Elastics-MacBook-Pro in ~/elastic/logstash-output-riemann on master*
$ be rspec ./spec/outputs/riemann_spec.rb:123
Using Accessor#strict_set for specs
Run options:
  include {:locations=>{"./spec/outputs/riemann_spec.rb"=>[123]}}
  exclude {:redis=>true, :socket=>true, :performance=>true, :couchdb=>true, :elasticsearch=>true, :elasticsearch_secure=>true, :export_cypher=>true, :integration=>true, :windows=>true}

outputs/riemann
  build_riemann_formatted_event
    when using a Json string, tags might be an ArrayList
      #receive will fail unless the ArrayList implements compact

Finished in 0.502 seconds (files took 0.534 seconds to load)
1 example, 0 failures

Randomized with seed 8914