Test results are condensed into changes in the system in such way that all intended improvements are met. PCB layout changes, components moved around inside the enclosure, ingress protection improvements, software bugs get fixed and/or any others that we find necessary to have a perfect prototype of the intended device in our hands the next time around.
When all changes are met at design level the Prototyping and Testing duo restarts. At this point we are confident that the product is as expected, and will perform perfectly in any scenario it is to do so.