> In the 1980s everything was written in assembly and you depending on the clock speed. However these days embedded should have learned that the CPU you write for will go out of production and so you should write portable code except for the small shim layers that talk to the real hardware.

Ah... the illusions of "portability". A lot of the reason you want to test your code is that there may be behaviors specific to the target platform (either in the hardware itself, in the compiler, in the runtime, or in support libraries/frameworks). You may well write with the intent to be portable, but you test for the reality that you never really are.