Hi there! So, you know how when you're playing with your toys or doing something, sometimes you just want to make sure everything is working okay before you really get into it? That's kind of what sanity testing is like.
When grown-ups make a new computer program or software, they want to make sure it's going to work properly before they let other people use it. So they do something called "sanity testing." They check to make sure that the program is doing the basic things it should be doing without any big problems.
For example, if they made a video game, they might check to make sure that when you start the game, you can see the instructions and that the buttons do what they're supposed to. They might also check to make sure that the game doesn't crash or freeze right away.
Sanity testing is just a quick check to make sure things are working like they should, so that they know they're not wasting their time testing something that's not even close to being ready. It's a little like taking a peek at your toys before you start playing -- just to make sure everything is looking good and ready to go!