$ python3 before/task_import.py sample-tasks.csv
Traceback (most recent call last):
  File "before/task_import.py", line 24, in <module>
    print(json.dumps(import_tasks(handle.read()), ensure_ascii=False, indent=2))
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "before/task_import.py", line 16, in import_tasks
    raise ValueError('duplicate task_id: ' + str(task_id))
ValueError: duplicate task_id: 7

exit_code=1
