Copy event subscriber from master

Author: p

spec/support/event_subscriber.rb

@@ -44,6 +44,13 @@ def started(event)
       end
     end
 
+    # Filters command started events for the specified command name.
+    def command_started_events(command_name)
+      started_events.select do |event|
+        event.command[command_name]
+      end
+    end
+
     # Locates command stated events for the specified command name,
     # asserts that there is exactly one such event, and returns it.
     def single_command_started_event(command_name)