Change the assertions in the config reloading spec

The assertions was using dummy outputs and kept received events into an
array in memory, but the test actually only needed to match the number
of events it received, this PR add a DroppingDummyOutput that wont
retain the events in memory.

The previous implementation was causing a OOM issue when running the
test on a very fast machine.

Fixes: #6335

Fixes #6346

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

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