The format could be Standard, Historic, Sealed or Alchemy
The best way I've found to test your deck is to just play
The game works just as well with two players as it does three, five, or however many are in your group
Way back when, Commander was called Elder Dragon Highlander, after the five original Elder Dragons ([mtg_card]Arcades Sabboth[/mtg_card], [mtg_card]Palladia-Mors[/mtg_card], [mtg_card]Vaevictis Asmadi[/mtg_card], [mtg_card]Nicol Bolas[/mtg_card], and [mtg_card]Chromium[/mtg_card]), whose tri-colored color identities helped shape the rules of the format
They'll be spread throughout booster packs for upcoming expansion The Brothers' War, a retelling of a classic Magic storyline from 1994 that will have its global release on November 18