The best and safest way (if you don't have a multimeter) is to use a torch battery, 3 pieces of wire and a torch globe. Attach wires to the centre terminal of the globe, & one to the globe base. Now cut the wire attached to the globe base and insert the torch battery between the cut ends.This creates a test circuit with the torch globe, & battery in series.There are now two wire ends free. To test your circuit, touch the two free wire end together. If you have done this right. the torch globe will light. To use your tester, touch one wire end to a pin on your shaver wall plug, touch the other wire to a hole in the shave end of shaver cable.If the globe does not light, try the other hole. If it still doesn't light, touch your tester wires together to test it's still working ok. Test the cable again, if no light, you have a broken power cable.
NOTES:
1. For this operation the razor and cable are NOT CONNECTED to the power outlet
2. Use insulated wire and solder them to the torch globe if you can, otherwise use a cheap globe holder from Tandy