Validate user add to the group are in the same course with group

app/models/course/group_user.rb

@@ -5,6 +5,8 @@ class Course::GroupUser < ActiveRecord::Base
 
   enum role: { normal: 0, manager: 1 }
 
+  validate :user_and_group_in_same_course
+
   belongs_to :user, inverse_of: :course_group_users
   belongs_to :course_group, class_name: Course::Group.name, inverse_of: :group_users
 
@@ -16,4 +18,9 @@ class Course::GroupUser < ActiveRecord::Base
   def set_defaults
     self.role ||= :normal
   end
+
+  def user_and_group_in_same_course #:nodoc:
+    return if user.courses.include?(group.course)
+    errors.add(:user, I18n.t('activerecord.errors.models.course_group_user.not_enrolled'))
+  end
 end

config/locales/en/activerecord/errors/models/course_group_user.yml

@@ -0,0 +1,6 @@
+en:
+  activerecord:
+    errors:
+      models:
+        course_group_user:
+          not_enrolled: 'user must be enrolled in same course as group'

spec/factories/course_group_users.rb

@@ -6,6 +6,12 @@
     creator
     updater
 
+    after(:build) do |group_user|
+      course = group_user.group.course
+      user = group_user.user
+      create(:course_user, course: course, user: user) unless user.courses.include?(course)
+    end
+
     factory :course_group_student
     factory :course_group_manager do
       role :manager

spec/models/course/group_user_spec.rb

@@ -3,4 +3,14 @@
 RSpec.describe Course::GroupUser, type: :model do
   it { is_expected.to belong_to(:user).inverse_of(:course_group_users) }
   it { is_expected.to belong_to(:course_group).inverse_of(:group_users) }
+
+  let!(:instance) { create(:instance) }
+  with_tenant(:instance) do
+    subject { build(:course_group_user) }
+
+    context 'when user is not enrolled in group\'s course' do
+      before { subject.user.course_users.delete_all }
+      it { is_expected.not_to be_valid }
+    end
+  end
 end