diff --git a/logstash-core/spec/logstash/agent_spec.rb b/logstash-core/spec/logstash/agent_spec.rb
index 2c4aa6d79..98eafba9d 100644
--- a/logstash-core/spec/logstash/agent_spec.rb
+++ b/logstash-core/spec/logstash/agent_spec.rb
@@ -411,19 +411,19 @@ describe LogStash::Agent do
     # We need to create theses dummy classes to know how many
     # events where actually generated by the pipeline and successfully send to the output.
     # Theses values are compared with what we store in the metric store.
-    class DummyOutput2 < LogStash::Outputs::DummyOutput; end
+    class DummyOutput2 < LogStash::Outputs::DroppingDummyOutput; end
 
-    let!(:dummy_output) { DummyOutput.new }
+    let!(:dummy_output) { LogStash::Outputs::DroppingDummyOutput.new }
     let!(:dummy_output2) { DummyOutput2.new }
     let(:initial_generator_threshold) { 1000 }
 
     before :each do
-      allow(DummyOutput).to receive(:new).at_least(:once).with(anything).and_return(dummy_output)
+      allow(LogStash::Outputs::DroppingDummyOutput).to receive(:new).at_least(:once).with(anything).and_return(dummy_output)
       allow(DummyOutput2).to receive(:new).at_least(:once).with(anything).and_return(dummy_output2)
 
       allow(LogStash::Plugin).to receive(:lookup).with("input", "generator").and_return(LogStash::Inputs::Generator)
       allow(LogStash::Plugin).to receive(:lookup).with("codec", "plain").and_return(LogStash::Codecs::Plain)
-      allow(LogStash::Plugin).to receive(:lookup).with("output", "dummyoutput").and_return(DummyOutput)
+      allow(LogStash::Plugin).to receive(:lookup).with("output", "dummyoutput").and_return(LogStash::Outputs::DroppingDummyOutput)
       allow(LogStash::Plugin).to receive(:lookup).with("output", "dummyoutput2").and_return(DummyOutput2)
 
       @abort_on_exception = Thread.abort_on_exception
@@ -435,7 +435,7 @@ describe LogStash::Agent do
       end
 
       # wait for some events to reach the dummy_output
-      sleep(0.01) until dummy_output.events.size > initial_generator_threshold
+      sleep(0.01) until dummy_output.events_received > initial_generator_threshold
     end
 
     after :each do
@@ -461,7 +461,7 @@ describe LogStash::Agent do
         subject.send(:"reload_pipeline!", "main")
 
         # wait until pipeline restarts
-        sleep(0.01) until dummy_output2.events.size > 0
+        sleep(0.01) until dummy_output2.events_received > 0
       end
 
       it "resets the pipeline metric collector" do
diff --git a/logstash-core/spec/support/mocks_classes.rb b/logstash-core/spec/support/mocks_classes.rb
index 3cdf0a6dc..5ae99a68f 100644
--- a/logstash-core/spec/support/mocks_classes.rb
+++ b/logstash-core/spec/support/mocks_classes.rb
@@ -48,4 +48,32 @@ module LogStash module Outputs
     def close
     end
   end
+
+  class DroppingDummyOutput < LogStash::Outputs::Base
+    config_name "droppingdummyoutput"
+    milestone 2
+
+    attr_reader :num_closes
+
+    def initialize(params={})
+      super
+      @num_closes = 0
+      @events_received = Concurrent::AtomicFixnum.new(0)
+    end
+
+    def register
+    end
+
+    def receive(event)
+      @events_received.increment
+    end
+
+    def events_received
+      @events_received.value
+    end
+
+    def close
+      @num_closes = 1
+    end
+  end
 end end