npn - How do I check a BJT transistor if it is still functional?

Is there a simple method to do a sanity check on a bipolar junction transistor whether it is still functional or defective?

^{simulate this circuit – Schematic created using CircuitLab}

Say for example I have a circuit that used to function, and I suspect the transistor (NPN, PNP). How would I go forward to make sure the transistor is defective or how can I reasonably be sure it isn't? Do I need the datasheet for the part?