The Tenser's transformation spell description (Xanathar's Guide to Everything, pg. 168) states:
You endow yourself with endurance and martial prowess fueled by magic. Until the spell ends, you can’t cast spells, and you gain the following benefits:
- You can attack twice, instead of once, when you take the Attack action on your turn. You ignore this benefit if you already have a feature, like Extra Attack, that gives you extra attacks.
The description of haste says:
Choose a willing creature that you can see within range. Until the spell ends, [...] it gains an additional action on each of its turns. That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.
If wizard A casts the spell Tenser's transformation on himself and wizard B casts haste on A, does this allow A to perform 4 attacks?
In other words: does the fact that haste gives an extra single Attack action prevent Tenser's transformation from triggering?