After JExpress builds your installers, you can quickly test, from JExpress' GUI, any installer which is compatible with the OS where JExpress is running. If there's only 1 compatible installer, then it will start when you click the Test button. Otherwise, you'll simply need select the installer you want to test.

If you're running JExpress on Windows 7, Windows 8 or Windows 10, then you'll need to install a 3rd party program called Elevate to test the installer's from JExpress' GUI.

You can also start the installer by using the desktop icon that JExpress created when it built your installers (assuming you have that option selected on the Test panel). And, finally, you can learn more about how to test on other computers.