A kung fu class would not be a kung fu class without combat.
Kung fu, however, is not about fighting - it is about self defence - and the two are rather different.

Fighting is about contesting yourself against another, besting them in combat and perhaps obtaining a prize.
Self defence is about escaping harm - using the minimum degree of effort and commitment.
There are no prizes or runners-up in self defence; if you lose in a real life confrontation, you could die.

Class practice must skirt the edge of reality; tasting the danger without running the risk of serious injury.