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

          [:setup, :cleanup, :teardown].each do |fixture|
            observer = lambda do |test_case, _, _, value, callback|
              if value.nil?
                test_case.send("unregister_#{fixture}_callback", callback)
              else
                test_case.send("register_#{fixture}_callback", callback, value)
              end
            end
            base.register_attribute_observer(fixture, &observer)
          end
        end