diff --git a/lib/fluent/test/driver/filter.rb b/lib/fluent/test/driver/filter.rb
index 0b8624857d..0d6adb13da 100644
--- a/lib/fluent/test/driver/filter.rb
+++ b/lib/fluent/test/driver/filter.rb
@@ -37,6 +37,10 @@ def filtered_records
           @filtered.map {|_time, record| record }
         end
 
+        def filtered_time
+          @filtered.map {|time, _record| time }
+        end
+
         def instance_hook_after_started
           super
           filter_hook = ->(time, record) { @filtered << [time, record] }