There are several factors that could cause a dryer to not tumble.
Here are several possibilities.
-Thermal fuse is bad
-Bad power to the dryer
-Dryer belt is broken
-Start switch is bad
To make accurate test some times a volt meter is worth having,if you plan to to repair many more appliances it may be worth investing in a cheap one from a local hardware store. Dryers especially are relatively simple to test using a meter.
When the fuse reads open it will stop supply voltage from reaching the motor. This fuse will usually fail when a overheat condition occurs. If you have found the dryer thermal fuse open investigate why the fuse has tripped.
Bad power to the unit will stop the drum from turning,with a volt meter ensure the washer has proper supply voltage.
Determining if the belt is broken is fairly simple open the top of the dryer and peek in. If there is not belt around the drum you found the issue.
When you press start and hear nothing you have a voltage or start switch issue. Like stated previously the thermal fuse will take the voltage to the motor out of the equation. By using the multimeter ohm setting you can ohm the start switch out and ensure there is some resistance.
If you hear the motor running and the drum is not turning the belt is broken.