Testing a microwave oven involves making sure the unit is working properly. You can run your own series of basic tests in just a few minutes. This will allow you to find out if its timer and cooking ability are working the way they're supposed to. If your microwave fails your own tests, you can then begin to troubleshoot to find the problem.
Fill a microwavable cup with water. Insert it into your microwave. Set your microwave for a "Normal" cooking mode (not "Low" or "High," if applicable) and set the timer for 60 seconds. Start your microwave. If your microwave is functioning properly, the water in your cup should begin to boil as the timer draws closer to 60 seconds.
Read the directions on a piece of microwavable food. Anything that can work in a microwave will work -- like a frozen french bread pizza or a microwavable soup container. Insert the food into your microwave, set the timer for the appropriate conditions and begin to cook your food. If your food begins to burn well before the packaging said it would, your microwave isn't working properly. The converse is true -- if you reach the recommended cooking time and your food isn't finished cooking, your microwave isn't working properly if you've properly followed the directions.
Turn on your microwave's "Cooking" mode and begin to run through the buttons on the LCD control panel, one by one. When you press the "Popcorn" button, for example, your microwave should begin to cook under its pre-programmed popcorn mode. Stop the microwave and continue on to the next setting. This will test to make sure that signals you input on the LCD screen or by pressing the buttons are making their way to the microwave's internal control chip. If certain buttons are non-responsive, your microwave is not working properly.