The test will not go through if you point to the disk. The steps to do the test are as follows:
1) Create a folder in your SSD, and share it with public
2) You will be asked Admin Username & Password
3) Now point your test to that folder and it will work
I tested it on a Mypassport SSD with USB-C interface, and the result was not that impressive for a 5 GB stress test, the SSD was also heated up. But, I think the test was too extreme you would not run the SSD to that stress level. Attached is screenshot, the manufacturer claimed 515MB/s but I got much lower speeds than that.