The topics Eyeless posted had me rereading the threshold sections, and lo and behold I screwed up my face and wondered how I missed this.
If a shooter has 1 hit on a standard Threshold of 1, then he has 0 net hits. It is still a successful test (assuming defense has already rolled and so on).
I know many if not most of you are thinking, "no shit".
However, coming from SR3; 1 success in the same scenario would be 1 net success. ie not enough to stage up the damage but it was successful.
So based on the thresholds in SR4 it is possible and not uncommon to have a 0 net hit successful test.
Except in the case of Direct Combat spells, where you must have 1 Net hit to have a successful test. Thinking this through, on a Direct Combat spell, 100% unresisted has a base Threshold of 1. Correct? So 1 hit on the casting would yield 0 net hits, the spell would fail. Indeed any Direct Combat spell must have 2 hits unresisted to succeed as this would be 1 net hit.
So any caster that is to cast such spell type really must be throwing 6 dice for an average chance of getting the spell to even go off unresisted. (yes I know 6 dice is nothing, but think of background counts and other modifiers.) If such modifiers reduce your Spell Pool to less than 6 chances are you might as well not even try that Direct Combat spell.
And all the above is assuming no resistance.
The question is, aside from Direct Combat spells and Detection spell are there any other tests that must have 1 net hit (or 2 hits min. on a standard Threshold).
Requires 1 net hit:
Direct Combat spell
Detection spell