I see this as a possible problem that would have to be considered when such an idea is implemented but not something that stops the idea dead in its tracks because it is fundamentally opposed to the principle of equality.

You would have to make sure that the tests are truly random (everyone has an equal chance of being selected), that they run only for a limited and pre-determined time which cannot be extended and that the differences to existing laws is not too big (e.g. people shouldn’t suddenly become multi-millionaires because some law was tested on them).

Such tests would then no more or less contribute to inequality than, say, jury duty.