Fix Active Model observer tests

activemodel/lib/active_model/observing.rb

@@ -52,6 +52,10 @@ module ActiveModel
         end
       end
 
+      def count_observers
+        @observer_instances.size
+      end
+
       protected
         def instantiate_observer(observer) #:nodoc:
           # string/symbol

activemodel/test/cases/observing_test.rb

@@ -121,13 +121,11 @@ class ObserverTest < ActiveModel::TestCase
     foo = Foo.new
     FooObserver.instance.stub = stub
     FooObserver.instance.stub.expects(:event_with).with(foo)
-    Foo.send(:changed)
     Foo.send(:notify_observers, :on_spec, foo)
   end
 
   test "skips nonexistent observer event" do
     foo = Foo.new
-    Foo.send(:changed)
     Foo.send(:notify_observers, :whatever, foo)
   end
 end