registrations are unique for exam,user pairs

Author: kylesferrazza

app/models/registration.rb

@@ -28,6 +28,17 @@ class Registration < ApplicationRecord
 
   validates :user, uniqueness: { scope: :exam_version }
 
+  validate :user_exam_uniqueness
+  def user_exam_uniqueness
+    other_reg_exists =
+      user
+      .registrations
+      .where(exam_version: exam.exam_versions)
+      .where.not(exam_version: exam_version)
+      .any?
+    errors.add(:user, 'already has a registration for another version of that exam') if other_reg_exists
+  end
+
   def room_version_same_exam
     return unless room
 

test/models/user_test.rb

@@ -18,4 +18,13 @@ class UserTest < ActiveSupport::TestCase
     assert_match(/has already been taken/, r2.errors.full_messages.to_sentence)
     assert_not r2.save
   end
+
+  test 'cannot create two registrations for the same Exam-User pair' do
+    r1 = create(:registration)
+    second_version = create(:exam_version, exam: r1.exam)
+    r2 = build(:registration, user: r1.user, exam_version: second_version)
+    assert_not r2.valid?
+    assert_match(/has a registration for another version/, r2.errors.full_messages.to_sentence)
+    assert_not r2.save
+  end
 end