Hey, once again!
Is it possible to make a Teamwork test with Spellcasting? I am aware that under certain circumstances like Ritual Spellcasting and/or Spirits involved it's possible: I am asking 'bout two spellcasters with a Spellcasting test.
This is a great question. After going through the rules for an admittedly short amount of time, I think the answer is no. The Teamwork Test rules are explicit about people being able to work together, and Spellcasting is explicitly about channeling mana through oneself as a force of will. I think it doesn't work for the same reason you can't get Teamwork on a Surprise Test or a Toxin Resistance Test--it's entirely internal.
This is one of my looser interpretations, though, and I only looked at the core rules. I'm certain that the rules as intended are that teamwork in Sorcery is Ritual Spellcasting.
Thanks!
At the same time, there's nothing really saying you can't, nor that you can't help someone else guide the flow of mana.
So, like most rules questions, the answer is... "Eh."
Leadership can, without a doubt, help on Spellcraft rolls. I find it less odd for Spellcraft to help Spellcraft rolls, though the fine details are a table call. To help someone cast a spell, do you need to know that same spell? Probably. If you help someone cast a spell, does that mean you take drain, too? I'd say yes, which can help mitigate the shenanigans of the party's mages teamworking with one another for every out-of-combat buff spell.
Rituals, meanwhile, have their own unique shenanigans that have entirely different effects from teamwork spellcasting. And has its own rules for teamwork ritual spellcasting. And ritual spellcasting can be done solo.