[ruby/yarp] Extract test listener to its own class

https://github.com/ruby/yarp/commit/c8caa997c0

test/yarp/dispatcher_test.rb

@@ -4,27 +4,27 @@ require_relative "test_helper"
 
 module YARP
   class DispatcherTest < TestCase
-    def setup
-      @listener = Class.new do
-        attr_reader :events_received
+    class TestListener
+      attr_reader :events_received
 
-        def initialize
-          @events_received = []
-        end
+      def initialize
+        @events_received = []
+      end
 
-        def call_node_enter(node)
-          @events_received << :call_node_enter
-        end
+      def call_node_enter(node)
+        events_received << :call_node_enter
+      end
 
-        def call_node_leave(node)
-          @events_received << :call_node_leave
-        end
-      end.new
+      def call_node_leave(node)
+        events_received << :call_node_leave
+      end
     end
 
     def test_dispatching_events
+      listener = TestListener.new
+
       dispatcher = Dispatcher.new
-      dispatcher.register(@listener, :call_node_enter, :call_node_leave)
+      dispatcher.register(listener, :call_node_enter, :call_node_leave)
 
       root = YARP.parse(<<~RUBY).value
         def foo
@@ -33,8 +33,7 @@ module YARP
       RUBY
 
       dispatcher.dispatch(root)
-
-      assert_equal([:call_node_enter, :call_node_leave], @listener.events_received)
+      assert_equal([:call_node_enter, :call_node_leave], listener.events_received)
     end
   end
 end