gistfile1.rbx

module ValidationTestHelper
  def assert_valid(field, *values)
    __model_check__
    values.flatten.each do |value|
      o = __setup_model__(field, value)
      if o.valid?
        assert_block { true }
      else
        messages = [o.errors[field]].flatten
        assert_block("unexpected invalid field <#{o.class}##{field}>, value: <#{value.inspect}>, errors: <#{o.errors[field].inspect}>.") { false }
      end
    end
  end
  
  def assert_invalid(field, message, *values)
    __model_check__
    values.flatten.each do |value|
      o = __setup_model__(field, value)
      if o.valid?
        assert_block("field <#{o.class}##{field}> should be invalid for value <#{value.inspect}> with message <#{message.inspect}>") { false }
      else
        messages = [o.errors[field]].flatten
        assert_block("field <#{o.class}##{field}> with value <#{value.inspect}> expected validation error <#{message.inspect}>, but got errors <#{messages.inspect}>") { messages.include?(message) }
      end
    end
  end
  
  def __model_check__
    raise "@model must be assigned in order to use validation assertions" if @model.nil?
    
    o = @model.dup
    raise "@model must be valid before calling a validation assertion, instead @model contained the following errors #{o.errors.instance_variable_get('@errors').inspect}" unless o.valid?
  end
  
  def __setup_model__(field, value)
    o = @model.clone
    attributes = o.instance_variable_get('@attributes')
    o.instance_variable_set('@attributes', attributes.dup)
    o.send("#{field}=", value)
    o
  end
end

gistfile2.rbx

 it 'should validate length of' do
    {
      :title => 255,
    }.each do |field, max|
      assert_invalid field, ('%d-character limit' % max), 'x' * (max + 1)
      #TODO: this line cannot work - as it used clone and slug must be uniq
      #assert_valid field, 'x' * max
    end
  end

  it 'should validate presence of' do
    [:title].each do |field|
      assert_invalid field, 'required', "", nil
    end
  end

  it 'should validate format of' do
    assert_valid :slug, 'abc', 'abcd-efg', 'abcd_efg', 'abc.html', '/', '123'
    assert_invalid :slug, 'invalid format', '!@£!@£$'
  end

  it 'should magic invalid slugs into valid ones' do
    assert_valid :slug, 'abcd efg' ' abcd', 'abcd/efg', '£$ test @£@£'
  end