There are a few ways to beat Test Your Might in Mortal Kombat X.
The first way is to use a character with long range attacks. Characters like Sub-Zero, Mileena, and Ermac all have moves that can hit opponents from afar. This will make it difficult for your opponent to get close enough to you to activate Test Your Might.
Another way to beat Test Your Might is to use a character with high mobility. Characters like Scorpion and Takeda can quickly close the distance between them and their opponents. This will give you an opportunity to attack before your opponent has a chance to activate Test Your Might.
Finally, you can also try to baiting your opponent into activating Test Your Might. If you know your opponent is looking for an opportunity to use Test Your Might, you can try bait them into using it by feigning an attack or by playing defensively. Once they've activated Test Your Mighty, you can then take advantage of the situation and attacking while they're vulnerable.