Add ProgrammingGroup & ProgrammingGroupMembership

* User can create programming group with other users for exercise
* Submission is shared in a group
* Also adjust specs

spec/policies/submission_policy_spec.rb

@@ -15,13 +15,23 @@ describe SubmissionPolicy do
 
   %i[download_file? render_file? run? score? show? statistics? stop? test?].each do |action|
     permissions(action) do
+      let(:exercise) { build(:math) }
+      let(:group_author) { build(:external_user) }
+      let(:other_group_author) { build(:external_user) }
+
       it 'grants access to admins' do
         expect(policy).to permit(build(:admin), Submission.new)
       end
 
       it 'grants access to authors' do
         contributor = create(:external_user)
-        expect(policy).to permit(contributor, build(:submission, exercise: Exercise.new, contributor:))
+        expect(policy).to permit(contributor, build(:submission, exercise:, contributor:))
+      end
+
+      it 'grants access to other authors of the programming group' do
+        contributor = build(:programming_group, exercise:, users: [group_author, other_group_author])
+        expect(policy).to permit(group_author, build(:submission, exercise:, contributor:))
+        expect(policy).to permit(other_group_author, build(:submission, exercise:, contributor:))
       end
     end
   end