$ bundle update

Bundler could not find compatible versions for gem "rack-test":
  In Gemfile:
    rails (= 3.0.10) depends on
      rack-test (~> 0.5.7)

    rack-test (0.6.1)




and le Gemfile:

gem 'rails',         '= 3.0.10'

group :test do
  gem 'cucumber-rails'
  gem 'capybara'
  gem 'launchy'
  gem 'database_cleaner'
  gem 'rack-test', '0.6.1'
end