Allow teachers to access internal users and manage them in their study groups

spec/policies/internal_user_policy_spec.rb

@@ -5,7 +5,7 @@ require 'rails_helper'
 describe InternalUserPolicy do
   subject(:policy) { described_class }
 
-  %i[create? edit? index? new? show? update?].each do |action|
+  %i[create? edit? new? show? update?].each do |action|
     permissions(action) do
       it 'grants access to admins only' do
         expect(policy).to permit(build(:admin), InternalUser.new)
@@ -16,6 +16,15 @@ describe InternalUserPolicy do
     end
   end
 
+  permissions :index? do
+    it 'grants access to admins and teachers only' do
+      expect(policy).not_to permit(build(:external_user), InternalUser.new)
+      %i[admin teacher].each do |factory_name|
+        expect(policy).to permit(create(factory_name), InternalUser.new)
+      end
+    end
+  end
+
   permissions :destroy? do
     context 'with an admin user' do
       it 'grants access to no one' do