diff --git a/test/plugin/test_out_buffer.rb b/test/plugin/test_out_buffer.rb
index afaac1bcdd..b683bea2b0 100644
--- a/test/plugin/test_out_buffer.rb
+++ b/test/plugin/test_out_buffer.rb
@@ -45,7 +45,7 @@ def create_driver(conf = "")
 
     time = event_time
     record = {"message" => "test"}
-    d.run(default_tag: 'test') do
+    d.run(default_tag: 'test', expect_emits: 1) do
       d.feed(time, record)
     end