test that update task id is correctly cached

test/test_job_routes.py

@@ -67,6 +67,10 @@ def test_job_update_all(client, mocker):
     jsonschema.validate(refresh_task_response, TASK_ID_RESPONSE_SCHEMA)
     assert refresh_task_response['task id'] == expected_task_id
 
+    db = backend_db()
+    assert db['classifier-cache:update-task-id'] \
+        == expected_task_id.encode('utf-8')
+
 
 def test_job_update_force_pending(client, mocker):
     expected_task_id = 'asf#asdf%111'