Testing Thumbnailator in Play (Scala)

To start off, let me just say that I am fairly new to Scala and Play. I've been tasked with writing tests for Thumbnailator. These tests are geared to make sure that images uploaded are resized to 400x400 from the CENTER of the image (was able to find solution to image position from: Using Thumbnailator, can i make thumbnail with same height and width regardless the image size).

I've seen unit tests in Scala before, but have not written anything to test a plugin. The plugin itself does not seem to have much documentation on how to test functionality. Is anyone smarter than myself able to provide me some guidance on how I would begin this?

Thank you.