I wanted to write something up about this card, because I've left some negative impressions on it in a different review and I want to clarify some things. I still think, for a LOT of investigators, this card is just worse than A Test of Will 1. Let's actually just break all 3 of them down for a second:
A Test of Will - Pay a card and a resource for the chance to cancel a revelation on a treachery.
A Test of Will 1 - Pay a card, a resource, and an experience point (proactively) to cancel a revelation on a treachery.
A Test of Will 2 - Pay a card to cancel a revelation on a treachery, with some chance that you will have to spend 2 XP after the scenario if you want to use it again.
The breakdown for me is pretty simple: most investigators who want this version will want to upgrade to the level 2 version. Investigators who want the level 1 version DO NOT AT ALL want this version or the level 2 version. This is almost centrally an issue of Willpower. Low will investigators can't pass these tests but are still personally crippled by encounter cards (think Preston Fairmont or Tony Morgan or Finn Edwards), and they will therefore take the level 1 version, probably later in the campaign, for some personal defense. Investigators who can consistently pass the will check have high will and are therefore less inclined to needing to cancel a treachery, so this becomes more of a support card at higher counts. Consistently being able to pass the check means that there's not much value in spending the 1 XP to guarantee the check passes, but it may be worth 2 XP for both the 1 resource savings and the insurance it provides you in cancelling one treachery you otherwise would've failed (the 1 XP version might do this if it so happens you purchase it right before the scenario you would have failed the check, but most of the time this wont be true). Obviously, by scenario 8, the level 1 iteration is almost strictly better than the level 2.
I say almost because there's one very easy to overlook side to this card, which is that, unlike Test of Will 1, it offers a test. That matters in Survivor because failing tests often means you get things. If you Take Heart a Test of Will test, you're usually happy regardless if it passes or fails. If you're Stella Clark in particular, Test of Will level 0 basically reads "1 card, 1 resource. On standard: 50/50 you either cancel the treachery or take an extra action this turn (and draw a card probably because Rabbit's Foot)". You could even intentionally Draw Thin to increase the odds of failure and make some extra cash (with DT and Rabbit's Foot, you recoup the cost of Test of Will and make back a resource). Now, this is all a bit less helpful in solo where you're less likely to encounter a treachery that doesn't already have a test most rounds, but in a group setting you could more quickly find a target, letting you either support a teammate, or at least profit for trying. These investigators are probably best off sticking to the level 0 version, as failing is not something you want to gamble 2 XP on.
All of that is to say, I think Test of Will level 0 is a pretty niche card. There are certainly some investigators that could use it for support, but it's very inconsistent support that isn't really recouped even with Rabbit's Foot out. I could see some versions of Agnes Baker or Patrice Hathaway running it as group support, sure. I think Stella Clark is by far the best home for it.