Coil testing procedures are described along with pictures in the honda manual. There are two different types of coils used on the 650s. One type can be tested with an Ohm meter. If you have the other you will need some special electronics lab equipment. There are drop sites on the web where you can look at the manual or copy it to your computer.
One easy way to test the coil is to swap it to the other side and see if the problem follows. Just unplug and switch both coils' primary leads and then switch the secondary leads to the oposite sides. Now the left coil is firing the right and the right coil is firing the left.
The manual also describes a way to test both the ignitor box and coil as a system by grounding one of the wires from the pickup. When it's removed from ground you get a spark at the plug.
The honda manual gives really good decriptions along with pictures on testing every part of the ignition system.