How to Test a Battery

My mom (she's quite handy) sent me this frugal tip on how to test a battery.  It is quite clever and could come in handy.  Is the flashlight broken or is the the battery?

Have a wonderful day!

Please take a peek at my shops to the right. :) Thanks!

UPDATE:  We have a little eyebrow trimmer that wasn't working well.  I took the battery out and found a new AAA one.  I tested it.  Sure enough the old one bounced and the new one didn't!  WOW!