Okay I know this is not new and people have discussed about it, but I still want to post something here to log the process.
To get in the Testmode, just connect to your DPT-S1 and create an empty file named "
rVPzp8O1j0m01oOq.crsZVu8crtmXGrc2". Then reboot it, press HOME key once to get back to the home. And then press MENU key four to six times (first time you press it you will see the time on top left corner). Then you will get into the Test Mode app. Online people said you need to press BACK button along with HOME key three times, but mine work with just pressing MENU buttons.
If you see black screen, just press once BACK button and you should be able to see Test Mode.
I think Sony updated the Test Mode in version 18.104.22.16880. My "Update Sony Reader file" shows "NG: file not found" instead of "sr.bin is not found".