In my profession, (medical/lab/pharma equipment technician) an internal test is NEVER considered proof a unit is correctly functioning. It must pass both internal, external and sometimes process challenge. If any one fails - it's no good. I am qualified by NIST (National Institute of Standards in Technology) as an instrumentation calibrator, so I feel I have some expertise on the subject. The problem with doing internal tests only are several:
1. Is the internal test complete? Does it test all components involved? The test circuitry was designed by the manufacturer of the radar/lidar. This could be a potential conflict. They want the equipment to appear reliable.
2. If the units internal time base / test circuit is not traceable to NIST standards, then it does not meet the current accepted standards for rigid, repeatable, scientific measurements. (And yes, the driving public should have a right to this level of verification and testing. If I get regulated government traceable standards when I buy an apple, I should also get the same or better where there are legal implications.)
3. If the lidar/radar has suffered an insult (drop/electrical surge etc.) the test circuitry has necessarily suffered the same.
4. It's tautological. The radar/lidar says itself is working, therefore it is. That is a logical fallacy. (Circular reasoning.)
If you go to the grocery store and use a scale, or buy gas, you will see a calibration sticker on the scale or pump. The same or greater standards should be used for law enforcement.
Therefore an external test to NIST traceable standards must be used in addition to any internal tests. Also, any internal tests should be approved by NIST as being able to conduct a reasonable test of the unit.
-PbFoot