Limit lookup scope for private callbacks.

Background: Commit 71937c0 introduced private callbacks, however, the use of "private_method_defined?" returns true all the way down the class hierarchy and thus causes trouble with a very common transition: Given an event "event :fail transitions_to :failed". If you don't explicitly define the "fail" event handler, "private_method_defined?" will still return true since Kernel#fail is defined for any object. Transitioning with "fail!" then causes a runtime error.

lib/workflow.rb

@@ -286,7 +286,7 @@ def run_action(action, *args)
     end
 
     def has_callback?(action)
-      self.respond_to?(action) or self.class.private_method_defined?(action)
+      self.respond_to?(action) or self.private_methods(false).map(&:to_sym).include?(action)
     end
 
     def run_action_callback(action_name, *args)

test/main_test.rb

@@ -311,6 +311,22 @@ def assign(args)
     a.assign!(args)
   end
 
+  test '#58 Limited private transition callback lookup' do
+    args = mock()
+    c = Class.new
+    c.class_eval do
+      include Workflow
+      workflow do
+        state :new do
+          event :fail, :transitions_to => :failed
+        end
+        state :failed
+      end
+    end
+    a = c.new
+    a.fail!(args)
+  end
+
   test 'Single table inheritance (STI)' do
     class BigOrder < Order
     end