You do not, if you use an RTOS that is already certified by the vendor. This saves not only a lot of time and effort for verification and validation, but also a

You do not, if you use an RTOS that is already certified by the vendor. This saves not only a lot of time and effort for verification and validation, but also a lot of risk, since validation is unpredictable and extremely expensive. Therefore it'd be remarkable not to see a certified RTOS in such industries and applications where that validation is required, like aerospace or medical.