Ensure start date year has 4 digits

app/forms/journeys/early_years_payment/provider/authenticated/start_date_form.rb

@@ -8,6 +8,7 @@ class StartDateForm < Form
           attribute :start_date, :date
 
           validates :start_date, presence: {message: i18n_error_message(:presence)}
+          validate :start_year_has_four_digits, if: -> { start_date.present? }
 
           def initialize(journey_session:, journey:, params:)
             super
@@ -30,6 +31,12 @@ def save
           def nursery_name
             EligibleEyProvider.find_by(urn: answers.nursery_urn)&.nursery_name
           end
+
+          def start_year_has_four_digits
+            if start_date.year < 1000
+              errors.add(:start_date, "Year must include 4 numbers")
+            end
+          end
         end
       end
     end

spec/forms/journeys/early_years_payment/provider/authenticated/start_date_form_spec.rb

@@ -23,6 +23,17 @@
 
   describe "validations" do
     it { should validate_presence_of(:start_date).with_message("Provide a date in the format 27 3 2024") }
+
+    context "when the year doesn't have 4 digits" do
+      let(:day) { 1 }
+      let(:month) { 1 }
+      let(:year) { 24 }
+
+      it "returns an error" do
+        subject.save
+        expect(subject.errors[:start_date]).to include("Year must include 4 numbers")
+      end
+    end
   end
 
   describe "#save" do