Index: lib/spec/rails/dsl/behaviour/base.rb
===================================================================
--- lib/spec/rails/dsl/behaviour/base.rb	(revision 2087)
+++ lib/spec/rails/dsl/behaviour/base.rb	(working copy)
@@ -35,10 +35,16 @@
         
         module ExampleMethods
           @@model_id = 1000
-          # Creates a mock object instance for a +model_class+ with common
-          # methods stubbed out.
-          # Additional methods may be easily stubbed (via add_stubs) if +stubs+ is passed.
-          def mock_model(model_class, stubs = {})
+          # Creates a mock instance for a +model_class+ with common methods
+          # stubbed out. Ancestor classes of +model_class+ may be given as
+          # additional arguments.
+          # Additional methods may be easily stubbed (via add_stubs) by passing
+          # a hash of method/value pairs as the final argument.
+          # example usage:
+          #   mock = mock_model(Manager, Employee, Person, :method => "value")
+          def mock_model(model_class, *args)
+            stubs = args.last.is_a?(Hash) ? args.pop : {}
+            class_hierarchy = [model_class] + args
             id = @@model_id
             @@model_id += 1
             m = mock("#{model_class.name}_#{id}")
@@ -48,7 +54,7 @@
             m.stub!(:errors).and_return(stub("errors", :count => 0))
             m.send(:__mock_proxy).instance_eval <<-CODE
               def @target.is_a?(other)
-                other == #{model_class}
+                #{class_hierarchy.inspect}.include?(other)
               end
               def @target.class
                 #{model_class}