I've yet to come across a way to test for everything. So no matter how much we test, and the more the better, there will always be that chance that something slips through, some error you just can't find until it goes to production.
There are techniques, tools and languages that can afford this but it requires a prohibitive amount of time. Prohibitive due to the distinct lack of life threatening risk as you say:
Fortunately for me, my mistakes won't cost someone their life.
(I am in a similar boat i.e. if I mess up no one dies - unless I believe the PM that they will kill me ;-))
-- Stop your grinnin' and drop your linen...they're everywhere!!!