At which point during the casting of this spell is the investigator to be affected chosen?

Is it before the Test, or after?

The reason I ask is because it says "If you pass, choose an Investigator ...", which seems to indicate it's after the roll, and only if successful.

The thing is, on the flip side of the card, for 0 successes, it says the chosen investigator becomes Cursed. The thing is, no Investigator was chosen in that case!

Question is, can I choose a different Investigator to be affected than the original I wanted to affect, after seeing the result of the die, or do I need to choose before rolling?

Flavourwise, it would be better to choose before the Test, but that's not what the card says.

I think in this case it's safe to assume, that you're indeed supposed to choose an Investigator beforehand, and that the wording just happened to be a little vague, which is unfortunate. At least it would make sense thematically. After all, you didn't cast that Spell for nothing, you must have had SOMEONE in mind, while channeling your magical energies.

The Errata mentions this, and says the investigator is chosen before.