Add 2 folders in a course: an empty folder and a folder with files and subfolders. In the app, check that you can see a download button next to the folder with files. Check that there's no button next to the empty folder. Click the download button. Check that it downloads all the files in the folder. Now add a new file in the folder or modify an existing one. In the app, do a PTR and check that there's a refresh button next to the folder. Check that clicking it downloads the new file.