# File test/test_params.rb, line 1639
    def test_argument_regexp
      init_arguments
      assert_equal(/foo/, @entry.args[4])
      @entry.set_arg_at(4, /bar/)
      assert_equal(/bar/, @entry.args[4])
      @entry.set_arg_at(4, nil) # allowed
      assert_exception(RuntimeError) {
        @entry.set_arg_at(4, 'foo') # not allowed
      }
    end