You can use a Needle type voltmeter. (NOT Digital type.) Measure the battery in Positive and Negative port. Then you will see the voltage become 3.0 - 4.0 V. 

In the meanwhile, you put a needle to short positive and negative. If the protection activate. The voltage will drop to zero immediately. Then you leave the measurement needle, after a second. Recheck the voltage again and you see the voltage back to 3.0-4.0V. It means the protection is reset after a second when you leave the short circuit needle.

If there is not protection. The voltage will keep the same and you feel the battery get hot in a second during you shorted the circuit. If it keep to shorted in long time, it will explosion.