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

races/urls.py

@@ -1,8 +1,8 @@
-from django.conf.urls import url
+from django.urls import path
 
 from races.views import index, race_detail
 
 urlpatterns = [
-    url(r'^$', index, name='races_index'),
-    url(r'^race/(?P<race_id>[A-Za-z0-9]+)/$', race_detail, name='race_detail'),
+    path('', index, name='races_index'),
+    path('race/<race_id>/', race_detail, name='race_detail'),
 ]