user_spec.rb

  context "without password confirmation" do
    before(:each) do
      subject.instance_eval do
        def password_confirmation
          self.password
        end
      end
    end
    it {should accept_values_for(:password, "abcdefg1")}
    it {should_not accept_values_for(:password, "Abcdefgh", "12345678")}
  end