valid attribute custom matcher for minitest

gistfile1.rb

class ValidAttributeMatcher
  def initialize(attr_name)
    @attr_name = attr_name
  end

  def matches?(subject)
    @subject = subject
    @subject.valid?
    @subject.errors[@attr_name].empty?
  end

  def failure_message_for_should
    "expected to valid ##{@attr_name} but #{@subject.errors[@attr_name]}"
  end

  def failure_message_for_should_not
    "expected to invalid ##{@attr_name} but valid"
  end
end

MiniTest::Unit::TestCase.register_matcher ValidAttributeMatcher, :have_valid_attribute