# File lib/test/unit/fixture.rb, line 5
        def included(base)
          base.extend(ClassMethods)

          [:setup, :cleanup, :teardown].each do |type|
            observer = lambda do |test_case, _, _, value, callback|
              if value.nil?
                test_case.fixture[type].unregister(callback)
              else
                test_case.fixture[type].register(callback, value)
              end
            end
            base.register_attribute_observer(type, &observer)
          end
        end