I have discovered that in the new test set, that was published recently, the new cards are presented, that are not mentioned in the train set.
Is this an intended situation, or a bug? Due to so many new cards, it may be considered as completely different games in the train and the test set, so I doubt the result can be estimated.
These cards are presented in the train set, but not in the test:
These cards are in the test set, but not in the train set (28 of them!):
Booty Bay Bodyguard
Dire Wolf Alpha
Lord of the Arena
Mana Tide Totem