def devaluate(actual, expected)
      failure_message = expected_message.size_of(actual).to_not_be(expected).not(actual.size)
      expected === actual.size ? fail(failure_message) : pass(new_message.is_size(expected))
    end
(see Riot::AssertionMacro#devaluate)
@param [Number] expected the unexpected size of actual