Cheapest priced copy (Duel Decks: Knights vs. Dragons): $0.35 at Card Kingdom, near mint, their price list as of .
Test of Faith 
Instant · Uncommon · Darksteel · #17
Prevent the next 3 damage that would be dealt to target creature this turn. For each 1 damage prevented this way, put a +1/+1 counter on that creature.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Duel Decks: Knights vs. Dragons | 28 | Uncommon | $0.35 | — |
| Darksteel | 17 | Uncommon | $0.35 | $0.49 |
| Modern Masters | 33 | Common | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 1 December 2004The +1/+1 counters are put onto the creature at the same time the damage is prevented. If a 1/1 creature would be dealt 6 damage, 3 damage is prevented and three +1/+1 counters are put on the creature. The creature ends up as a 4/4 creature with 3 damage marked on it.