There is a way to test, millions of compressors are rebuilt everyday around the world - its a whole industry.
Its spun with an electric motor and tested with a refrigerant to see if it can pump up to 350 psi head pressure. Its also checked for leaks in a bath with static pressure.
The pwm unit can be manually cycled with a signal generator (some tooling brands sell it as a unit now) and it can be built with some low cost components too)
The cars own system can be checked with a scanner that can dig into those PIDs, and can be further checked with an oscilloscope, very easy everyday regular work for any workshop.
Dumbasses call it “failed” because they dont know how it works or even how to test them, i bet most are still baffled by the old pressure regulated valve compressor that first came into production in the late 1980s (nearly 45 years ago)