update urls.pyes to use path() and add some tests

countdown/urls.py

@@ -1,5 +1,6 @@
 """URL patterns for the countdown views."""
-from django.conf.urls import include, url
+from django.conf.urls import include
+from django.urls import path
 from rest_framework.routers import DefaultRouter
 
 from countdown.views import CountdownItemViewSet
@@ -8,5 +9,5 @@ router = DefaultRouter()
 router.register(r'items', CountdownItemViewSet)
 
 urlpatterns = [
-    url(r'^api/', include(router.urls)),
+    path('api/', include(router.urls)),
 ]