does anyone know where you can set the test mode for the paypal module?

I have install of Zencart. I need to be able to set the definition MODULE_PAYMENT_PAYPAL_TESTING accordingly. I can see all the tests for it within the code and according to this thread its set within the db:

I just can't for the life of me figure out where you set/unset it? I imagine it should be in :

admin -> modules -> payment -> Paypal IPN

But it ain't. Have I missed something obvious?