while loop like that is infinite - it never exits. If it never exits, then the
_process() function can never end. Since
_process() is called every frame, you have now locked up the application and no more frames will ever be executed.
This is the case in most graphical applications, where you already have a central loop running the core processes of the application. Instead of using a
while loop you should ask yourself what you're trying to accomplish. For example, if you just wanted to print "test" over and over again, you could just do this:
Now when you run the game, your output panel will be flooded with "test" prints every 1/60 of a second.