Add submission deadline to exercises and allow teachers to view their submissions

spec/policies/external_user_policy_spec.rb

@@ -3,7 +3,7 @@ require 'rails_helper'
 describe ExternalUserPolicy do
   subject { described_class }
 
-  [:create?, :destroy?, :edit?, :index?, :new?, :show?, :update?].each do |action|
+  [:create?, :destroy?, :edit?, :new?, :show?, :update?].each do |action|
     permissions(action) do
       it 'grants access to admins only' do
         expect(subject).to permit(FactoryBot.build(:admin), ExternalUser.new)
@@ -13,4 +13,16 @@ describe ExternalUserPolicy do
       end
     end
   end
+
+  [:index?].each do |action|
+    permissions(action) do
+      it 'grants access to admins and teachers only' do
+        expect(subject).to permit(FactoryBot.build(:admin), ExternalUser.new)
+        expect(subject).to permit(FactoryBot.build(:teacher), ExternalUser.new)
+        [:external_user].each do |factory_name|
+          expect(subject).not_to permit(FactoryBot.build(factory_name), ExternalUser.new)
+        end
+      end
+    end
+  end
 end