I disagree. In theory no testing is necessary. If the insulation is so thin, that every product needs to be tested, then the design is marginal and isn't safe to begin with. It should be redesigned so it will comfortably exceed the minimum requirements.
Electrical safety can be guaranteed, purely by design. The breakdown voltage of various insulating materials is a well known parameter. All one needs to do is make sure the material is thick enough, sufficiently mechanically robust and large enough creapage and clearances are used throughout the design. In reality it may be necessary to test a small sample of materials/products, to ensure they meet the specifications but 100% testing is not desirable. Any products which have been subjected to the high potential test should be destroyed and not sold to the customer.
For sure, you have not the least experience in quality control of electricity and power electronics gears to write such a bullshit.
Should you be quality control manager, the first customer who will be electrocuted will send you to jail , and for a very long time.
For exemple, technical specifications of a SMPS...High pot tested at 4242Vdc 1m between primary and secondary.
You're talking nonsense. For a start, there's nothing in that data sheet to say that every single device has been tested, just that it can withstand 4242V, from primary to secondary and that the design (not necessarily every single model) has been tested to comply with various safety standards.
Safety can be guaranteed by design. There are far more potentially dangerous things, than a mains powered switching regulator, which are engineered to be safe and never tested to the design limits. Take a house for example, the supporting structures in the building, will be designed to hold the maximum nominal load, multiplied by a large safety factor (typically two), but it will never be tested to confirm this. The engineer who designed the building, ensured that it will be strong enough and conform to the relevant building regulations. The same is true for cars, aeroplanes, bridges, etcetera.
Testing can be useful to verify a design meets certain requirements (safety being only one of them) but once that's been achieved, it only needs to be done sporadically, to confirm the suppliers and manufacturing process are adequate. It's not necessary or desirable repeat tests, which are potentially dangerous. I certainly wouldn't want to live in a house, which has been tested right up to the design stress limits, that could cause microscopic cracks to form. I'd rather live in a house which has been designed to be safe and not subjected to unnecessary stress.