flags.Usage is introduced on page 32. On Page 35, if the reader leaves that code in their application, the ListTasks test will fail because the output will still include the flags.Usage text since that executes for a list command.
It’s probably easier to tell the reader to dump the flags.Usage since it has no bearing on the application and can easily be deleted or commented out for future reference and therefore won’t affect the testing revision on page 35.