luloo117117,
Mmantunes comment regarding the various requirements from the various international standards applies. Review the market where your product is to be shipped. Also, review the requirements of your customers if they are applicable. Some may require that prior to distributing product that you perform various safety and performance tests.
As Mmantunes comments, the hi-pot test can be considered a destructive test if design thresholds are exceeded. This is why many manufacturers rely on the design verification and validation of their equipment combined with the validated process with which it is manufactured. Product marking (e.g. UL, CSA) from a design perspective and site audits by these agencies, your registrar, and the government agency work together to establish a degree of confidence that the product manufactured is safe and effective.
Regarding the supplier tests that are performed, consider if they are validated test and manufacturing processes. If they aren't, then you will likely have to perform the test if it is a requirement. And as Mmantunes points out, understand what the effects of these tests on the finished device are. I once saw a product recall as a result, in part, of the process of testing that required repeat exercising of a component that resulted in premature failure. Understand the effects of your test and inspection program.
Good luck!
Kevin