You should be swapping out the Dropbox parts for mocks, which return ideal responses - you shouldnt ever test more code than absolutely necessary in a unit test, and that includes third party libraries or integrations.
If the Dropbox part fails, thats an entirely different ball game, but you should be assuming the response your unit tests requires, which means successes and failures as you test those parts of your code.
We love to learn from the educators who use Dropbox. Whether you teach kids, teens, adults or a combination of all three, we want to know what apps and integrations you use with Dropbox to help with teaching. Which of the ones below is your favorite, or most used tool?