validates :mobile_carrier, :presence => true, :if => Proc.new {|v|
v.mobile_phone.present?}

----------------

it { should validate_presence_of(:mobile_carrier, :if => Proc.new {|v|
v.mobile_phone.present?})}

You would do something like this:

describe MyModel
  context "when mobile phone is present" do
    subject { MyModel.new(:mobile_phone => true) }
    it { should validate_presence_of :mobile_carrier }
  end

  context "when mobile phone is not present" do
    subject { MyModel.new(:mobile_phone => false) }
    it { should_not validate_presence_of :mobile_carrier }
  end
end

I haven't tried this and I don't remember if the should_not works on
the validates_* properly.

I've always been partial to the way Datamapper handles things with
contextual validations.

You can get more sophisticated if you use the let() feature in Rspec.

Hope this helps.

Ho-Sheng Hsiao

On Aug 19, 11:18 pm, ericindc <ericmilf...@gmail.com> wrote: