Neal,
Yes, the CDI unit can be checked on a bench for proper operation ... and if NTF [no trouble found] that means one or more connections in the wiring harness need to be cleaned and treated with silicone grease to eliminate future corrosion problems!
Here are some threads with Bosch publications and additional info on component testing, theory of operation, etc. pertaining to the CDI system:
1.
http://forums.pelicanparts.com/showthread.php?threadid=226517&highlight=cdi+history
2.
http://forums.pelicanparts.com/showthread.php?threadid=160537&highlight=bosch+power
3.
http://forums.pelicanparts.com/showthread.php?threadid=173895&highlight=discrete+components
4.
http://forums.pelicanparts.com/showthread.php?threadid=158541
No, the old Bosch CDI units DO NOT 'wear out' in any sort of fashion!!! Components such as capacitors, Zener diodes, transistors, SCRs fail, yes, but can be replaced with reasonable ease. What it takes to troubleshoot a CDI unit is knowledge of discrete logic circuitry, and test equipment usage.
The most likely failure scenario for a CDI unit is a bad connection due to corrosion, loose connector, etc.