Read from the World of Warcraft client build files.
How Spiritwalker's Tunic Compares
Who It Suits
Mail is the armor type Evoker, Hunter and Shaman wear. With Agility or Intellect, Spiritwalker's Tunic suits Beast Mastery, Marksmanship and Survival Hunter; Elemental, Enhancement and Restoration Shaman; Devastation, Preservation and Augmentation Evoker.
Transmog Sets
Spiritwalker's Tunic is part of the transmog set Spiritwalker's Regalia (Shaman only). The other 16 pieces:
Built from the World of Warcraft client build files and recorded Auction House snapshots.
Where Spiritwalker's Tunic Fits
Other Items Named Spiritwalker's Tunic
2 other items in the current build are also called Spiritwalker's Tunic. Same-name entries are usually a different rank, faction, quest stage or reward track of the same object.
Blizzard numbers items as they are created, so the named items next to ID 78820 (78815 to 78825) were usually added in the same batch as Spiritwalker's Tunic: the same quest line, zone, vendor or reward set.