define singleton methods rather than adding and removing methods

activerecord/test/cases/transactions_test.rb

@@ -121,50 +121,39 @@ def test_update_attributes_should_rollback_on_failure!
   end
 
   def test_cancellation_from_before_destroy_rollbacks_in_destroy
-    add_cancelling_before_destroy_with_db_side_effect_to_topic
-    begin
-      nbooks_before_destroy = Book.count
-      status = @first.destroy
-      assert !status
-      assert_nothing_raised(ActiveRecord::RecordNotFound) { @first.reload }
-      assert_equal nbooks_before_destroy, Book.count
-    ensure
-      remove_cancelling_before_destroy_with_db_side_effect_to_topic
-    end
+    add_cancelling_before_destroy_with_db_side_effect_to_topic @first
+    nbooks_before_destroy = Book.count
+    status = @first.destroy
+    assert !status
+    @first.reload
+    assert_equal nbooks_before_destroy, Book.count
   end
 
-  def test_cancellation_from_before_filters_rollbacks_in_save
-    %w(validation save).each do |filter|
-      send("add_cancelling_before_#{filter}_with_db_side_effect_to_topic")
-      begin
-        nbooks_before_save = Book.count
-        original_author_name = @first.author_name
-        @first.author_name += '_this_should_not_end_up_in_the_db'
-        status = @first.save
-        assert !status
-        assert_equal original_author_name, @first.reload.author_name
-        assert_equal nbooks_before_save, Book.count
-      ensure
-        send("remove_cancelling_before_#{filter}_with_db_side_effect_to_topic")
-      end
+  %w(validation save).each do |filter|
+    define_method("test_cancellation_from_before_filters_rollbacks_in_#{filter}") do
+      send("add_cancelling_before_#{filter}_with_db_side_effect_to_topic", @first)
+      nbooks_before_save = Book.count
+      original_author_name = @first.author_name
+      @first.author_name += '_this_should_not_end_up_in_the_db'
+      status = @first.save
+      assert !status
+      assert_equal original_author_name, @first.reload.author_name
+      assert_equal nbooks_before_save, Book.count
     end
-  end
 
-  def test_cancellation_from_before_filters_rollbacks_in_save!
-    %w(validation save).each do |filter|
-      send("add_cancelling_before_#{filter}_with_db_side_effect_to_topic")
+    define_method("test_cancellation_from_before_filters_rollbacks_in_#{filter}!") do
+      send("add_cancelling_before_#{filter}_with_db_side_effect_to_topic", @first)
+      nbooks_before_save = Book.count
+      original_author_name = @first.author_name
+      @first.author_name += '_this_should_not_end_up_in_the_db'
+
       begin
-        nbooks_before_save = Book.count
-        original_author_name = @first.author_name
-        @first.author_name += '_this_should_not_end_up_in_the_db'
         @first.save!
-        flunk
-      rescue
-        assert_equal original_author_name, @first.reload.author_name
-        assert_equal nbooks_before_save, Book.count
-      ensure
-        send("remove_cancelling_before_#{filter}_with_db_side_effect_to_topic")
+      rescue ActiveRecord::RecordInvalid, ActiveRecord::RecordNotSaved
       end
+
+      assert_equal original_author_name, @first.reload.author_name
+      assert_equal nbooks_before_save, Book.count
     end
   end
 
@@ -475,14 +464,12 @@ def define_callback_method(callback_method)
     end
 
     %w(validation save destroy).each do |filter|
-      define_method("add_cancelling_before_#{filter}_with_db_side_effect_to_topic") do
-        Topic.class_eval <<-eoruby, __FILE__, __LINE__ + 1
-          remove_method :before_#{filter}_for_transaction
-          def before_#{filter}_for_transaction
-            Book.create
-            false
-          end
-        eoruby
+      define_method("add_cancelling_before_#{filter}_with_db_side_effect_to_topic") do |topic|
+        meta = class << topic; self; end
+        meta.send("define_method", "before_#{filter}_for_transaction") do
+          Book.create
+          false
+        end
       end
 
       define_method("remove_cancelling_before_#{filter}_with_db_side_effect_to_topic") do