If you're like me and you run a software that requires 'unsigned' windows drivers to function properly, in my case the software I'm running is Librecrypt which is very useful as it enables me to mount my LUKS-encrypted hard drive on a Windows system.
To enable Test Mode on Windows, open an elevated command prompt (Press Start->Search->cmd then right-click on it and click Run as administrator) and enter the following command:
bcdedit /set testsigning on
and reboot after running the command above
To disable Test mode, open an elevated command prompt as above and enter the following command:
bcdedit /set testsigning off
and also reboot after running the above command
Once you reboot, there would be a watermark message as shown below that would confirm that Test Mode is on.