A famous astronomer, Johann Zöllner, came up with a number of different tests designed to show that a person has the power to go into four-dimensional space. See if you can pass one!
Johann Zöllner has an optical illusion and a crater on the moon named after him, and he didn't get either by being a slouch in the science department. He worked out details about how Doppler shift affects light, and made measurements of the sun's light that actually hold up well against modern values.
Unfortunately for him, he was passionately interested in the spiritualism movement of the mid-1800s. This would have been fine as a personal matter, but he wrote about it, which earned him snickering from his peers. What's interesting is he came up with a hypothesis about how the spirits might do what they do - levitating things or whispering to someone while being invisible to others. He thought that the spirits might live in the fourth dimension, invisible to us, but able to change things in our dimension and easily as we could alter a two-dimensional drawing by doodling on it. Many spiritualists claimed this as well.
The difference between the scientists and spiritualists was that Zöllner came up with an idea about how to test these claims. He worked out that, if anyone was in the fourth dimension, they would be able to perform a few simple feats.
First, they would be able tie a knot in a solid loop of rope. If you were to put an untangled piece string down a piece of paper (representing a two dimensional universe), there is no way to tie the string in a knot. Only if you lift the ends off the piece of paper and into the third dimension can you knot it. Four-dimensional beings would be able to reach into a closed loop of string, pull part of it into their plane, and knot it.
Zöllner also proposed linking and unlinking solid wooden rings. That, we have seen magicians do, though I imagine they aren't reaching into the fourth dimension to do it. There's also flipping the spiral of a seashell - as easy a task as turning over a piece of paper for a fourth dimensional being. And finally - and this might take a little doing - Zöllner suggested reversing the structure of dextro tartaric acid. The molecule is shaped so that it polarizes light a certain way. A fourth dimensional being would be able to flip the structure, and have the molecule polarize light the opposite way. This we don't see in magic acts very often (although it would be a show-stopper, I'm sure).
No one has passed Zöllner's tests, so far. But don't give up. The next time you see a seashell, or a couple of solid rings, or a ponytail holder, or a bit of dextro tartartic acid (it's in fruits like grapes and bananas, so if you're healthy you should come across it pretty often), go ahead and try flexing your fourth dimensional muscles. And when you do, write in!