Return empty list when there are no users for the service.

Added a test for when there are no users for the service.
Added a test_url_for - do we want to add this test and use url_for in our tests?
Or explictly write the url in the test?

tests/app/service/test_rest.py

@@ -366,3 +366,25 @@ def test_get_users_by_service(notify_api, notify_db, notify_db_session, sample_u
             assert result['data'][0]['name'] == sample_user.name
             assert result['data'][0]['email_address'] == sample_user.email_address
             assert result['data'][0]['mobile_number'] == sample_user.mobile_number
+
+
+def test_get_users_for_service_returns_empty_list_if_no_users_associated_with_service(notify_api,
+                                                                                      notify_db,
+                                                                                      notify_db_session,
+                                                                                      sample_service,
+                                                                                      sample_user):
+    with notify_api.test_request_context():
+        with notify_api.test_client() as client:
+            sample_service.users.remove(sample_user)
+            auth_header = create_authorization_header(
+                path='/service/{}/users'.format(sample_service.id),
+                method='GET'
+            )
+
+            response = client.get(
+                '/service/{}/users'.format(sample_service.id),
+                headers=[('Content-Type', 'application/json'), auth_header]
+            )
+            assert response.status_code == 200
+            result = json.loads(response.get_data(as_text=True))
+            assert result['data'] == []

tests/app/service/test_url_for.py

@@ -0,0 +1,40 @@
+import uuid
+
+from flask import url_for
+
+service_id = str(uuid.uuid4())
+
+
+def test_url_for_get_services(notify_api):
+    with notify_api.test_request_context():
+        url = url_for('service.get_services')
+        assert str(url) == '/service'
+        url_with_user_id = url_for('service.get_services', user_id=1)
+        assert str(url_with_user_id) == '/service?user_id=1'
+
+
+def test_url_for_get_service_by_id(notify_api):
+    with notify_api.test_request_context():
+        url = url_for('service.get_service_by_id', service_id=service_id)
+        assert str(url) == '/service/{}'.format(service_id)
+
+        url_with_user_id = url_for('service.get_service_by_id', service_id=service_id, user_id=1)
+        assert str(url_with_user_id) == '/service/{0}?user_id={1}'.format(service_id, 1)
+
+
+def test_url_for_create_service(notify_api):
+    with notify_api.test_request_context():
+        url = url_for('service.create_service')
+        assert str(url) == '/service'.format(service_id)
+
+
+def test_url_for_update_service(notify_api):
+    with notify_api.test_request_context():
+        url = url_for('service.update_service', service_id=service_id)
+        assert str(url) == '/service/{}'.format(service_id)
+
+
+def test_url_for_renew_api_key(notify_api):
+    with notify_api.test_request_context():
+        url = url_for('service.renew_api_key', service_id=service_id)
+        assert str(url) == '/service/{}/api-key'.format(service_id)