Jean-Christophe, In order to apply your diff from the Rails ticket and to make sure that mixin_nested_set_test still works, I imported the ActiveRecord source code into a vendor directory in repository and copied the test directory into test/activerecord. But then when I looked at the Rakefile, I noticed the following task. desc ''Test the better_nested_set plugin.'' Rake::TestTask.new(:test) do |t| t.libs << ''lib'' t.test_files = [''test/preload_active_support.rb''] + FileList[''test/t_*.rb''] + FileList[''lib/*.rb''] t.verbose = true end How does your approach to running the tests compare to mine? Do you have the test files referenced in the task? thanks, Tim