Working with transistor will need you to test transistor.
some time even you will salvage transistor and u want to know whether they work or not .
well this can be done by this circuit .
This is basically a high gain amplifier
with feedback that causes the LED to flash at a rate determined by the 10u and 330k resistor. Remove one of the transistors and insert the unknown transistor. When it is NPN with the pins as shown in the photo, the LED will flash. To turn the unit off, remove one of the transistors.