Fix assertions when we catch an error in the tests

Code that is within a `with Python.raises(...)` context manager but
comes after the line that raises the exception doesn't get evaluated.
We had some assertions that we never being tested because of this, so
this ensures that they will always get run and fixes them where
necessary.

tests/app/dao/test_services_dao.py

@@ -293,17 +293,21 @@ def test_dao_add_user_to_service_ignores_folders_which_do_not_exist_when_setting
 
 
 def test_dao_add_user_to_service_raises_error_if_adding_folder_permissions_for_a_different_service(
-    sample_user,
     sample_service,
 ):
+    user = create_user()
     other_service = create_service(service_name='other service')
     other_service_folder = create_template_folder(other_service)
     folder_permissions = [str(other_service_folder.id)]
 
+    assert ServiceUser.query.count() == 2
+
     with pytest.raises(IntegrityError) as e:
-        dao_add_user_to_service(sample_service, sample_user, folder_permissions=folder_permissions)
-        assert 'insert or update on table "user_folder_permissions" violates foreign key constraint' in str(e.value)
-        assert ServiceUser.query.count() == 0
+        dao_add_user_to_service(sample_service, user, folder_permissions=folder_permissions)
+
+    db.session.rollback()
+    assert 'insert or update on table "user_folder_permissions" violates foreign key constraint' in str(e.value)
+    assert ServiceUser.query.count() == 2
 
 
 def test_should_remove_user_from_service(notify_db_session):