Fix tests.

problem/urls/admin.py

@@ -4,6 +4,6 @@ from ..views.admin import ContestProblemAPI, ProblemAPI, TestCaseUploadAPI
 
 urlpatterns = [
     url(r"^test_case/upload/?$", TestCaseUploadAPI.as_view(), name="test_case_upload_api"),
-    url(r"^problem/?$", ProblemAPI.as_view(), name="problem_api"),
+    url(r"^problem/?$", ProblemAPI.as_view(), name="problem_admin_api"),
     url(r"^contest/problem/?$", ContestProblemAPI.as_view(), name="contest_problem_api")
 ]