using_constants for rspec tests

gistfile1.rb

module Spec
  module Extension
    def using_constants(klass, new_constants)
      old_constants = {}
      begin
        new_constants.each_pair do |name, value|
          old_constants[name] = klass.__send__(:remove_const, name)
          klass.const_set(name, value)
        end

        yield
      ensure
        old_constants.each_pair do |name, value|
          klass.__send__(:remove_const, name)
          klass.const_set(name, value)
        end
      end
    end
  end
end

ActiveSupport::TestCase.__send__(:include, ::Spec::Extension)