How do I test a bridge rectifier?
Like drxzcl says they're of little use without datasheet. The square types usually can handle quite a few amperes, but you can't say if that will be 5 or 10.
To give you an idea of the possible range, this rectifier is about 1 inch square and available at current ratings from 12 A to 35 A:  



Nevertheless you can easily find out how the diodes are connected if you have a multimeter at hand. The multimeter usually has a diode test function: 



When the test probes are connected as shown the meter gives you the diode voltage drop, it the probes are switched you'll get an open connection indication.



So suppose you connect the + to one pin, and try the - on the others. If you have a reading on two of the pins that means that the + is connected to the left pin of the rectifier shown. You can verify this by placing the - on the remaining pin and check the two other pins again. You should again get a reading for both. Then the - is the right pin in the drawing. The other pins may be mutually switched.