This drill relies on the exhaustion caused by multiple repetitions. The drill is very simple, involving sprinting between posts, then making a full stretch diving save. Rinse-repeat.
The keepers line up on one post, while the coach positions to shoot at the same corner of the goal. The keeper sprints to touch the far post.

Once the post is touched, the coach reads to take a shot into the (now-) far corner of the goal.

The keeper has to make a full-stretch dive to attempt to make the save.

The process is repeated for 3-6 times before a new keeper tales over or a short rest is allowed.
The emphasis of the drill is the speed of the dive and the economic use of energy between shots. After 3-4 shots the keeper will be tired and strained. Check for enthusiasm and commitment to the later shots, as fatigue takes it’s toll.
A slight variation allows the coach to follow up with a second shot, giving the keeper a very brief moment to recover from the first. Normally the second shot will be back towards the other side of the goal.
Tips for coaches – Confidence Cohesion Technique
Any coach can utilize these drills with their keeper. The objectives are the same – enhance footwork, follow the ball better with the eyes, and judge the flight of the ball. Exercising the brain should be a core part of all soccer practices, forcing the athletes to make decisions under stress.
A coach can use any one of the drills independently, and involve multiple players, especially attackers, to sharpen their skills too.
Try to encourage the keeper to use these skills – their footwork, their eyes and reflexes, and be brave to make the judgement calls and decisions that will come up regularly in games.