You need to have a LED and 220 ohm resistor and a transistor to perform this test.
Now do as it has been explained below.At first Connect the LED, 220 ohm resistor and transistor as shown in the photo.
There should be no loose connection in the circuit.
Please check that transistor used is properly functioning.
You will not get any shock so don't have a fear in touching the wire.
Touch the top point with two fingers of one hand and the lower point with
fingers of the other hand and squeeze.
The LED will turn on brighter when you squeeze harder.
why this LED turned on?
Your body has resistance and when a voltage is present, current will flow though your body (fingers). The transistor is amplifying the current through your fingers about 200 times and this is enough to illuminate the LED.
you can make it one of by squeezing your fingers.