You need a test in order to enter the USVI (St. Thomas, St. John, St. Croix, Water Island, etc.). You do not need a test to move around within the USVI (i.e., from St. John to St. Thomas) and you do not need a test to return to the mainland U.S. (unless your home state has a requirement I am not aware of). In order to enter the USVI you must "apply" through their online portal - go to https://usviupdate.com/ for more information and a link to the portal.