Validate SessionDate#value

This adds validate to ensure that the date of the session is within the
academic year of the session.

app/models/session_date.rb

@@ -22,5 +22,22 @@ class SessionDate < ApplicationRecord
 
   belongs_to :session
 
-  validates :value, uniqueness: { scope: :session }
+  validates :value,
+            uniqueness: {
+              scope: :session
+            },
+            comparison: {
+              greater_than_or_equal_to: :earliest_possible_value,
+              less_than_or_equal_to: :latest_possible_value
+            }
+
+  private
+
+  def earliest_possible_value
+    Date.new((session || Date.current).academic_year, 9, 1)
+  end
+
+  def latest_possible_value
+    Date.new((session || Date.current).academic_year + 1, 8, 31)
+  end
 end

spec/models/session_date_spec.rb

@@ -18,7 +18,17 @@
 #  fk_rails_...  (session_id => sessions.id)
 #
 describe SessionDate do
-  subject(:session_date) { build(:session_date) }
+  subject(:session_date) { build(:session_date, session:) }
 
-  it { should be_valid }
+  let(:session) { create(:session, academic_year: 2024) }
+
+  describe "validations" do
+    it "validates that the date is within the academic year" do
+      expect(session_date).to validate_comparison_of(
+        :value
+      ).is_greater_than_or_equal_to(
+        Date.new(2024, 9, 1)
+      ).is_less_than_or_equal_to(Date.new(2025, 8, 31))
+    end
+  end
 end