Just to elaborate (though briefly from my phone) the setup and tear down are useful when working with memory buffers or simulating peripherals or HW to put everything into a known state before and after a set of tests and avoid duplicating code or complex setups again and again.
You can of course manually call a custom function before and after each test though and if people think it's not useful to automatically call and avoid a couple lines in each test I'm ok with skipping it ... it's just an option I found myself looking for migrating old test code to mynewt but hardly critical. K.
