A regression test suite is a set of tests aimed at ensuring that design functionality which once “worked” does not “regress” to a point where it does not work.

    For example let’s say that you have your Gigabit interface working in RX mode. You can create a regression test or suite of tests which check the functionality in RX mode: main-path, short and long packets, error conditions (rx error, collision (if allowed) etc.), encoding in XAUI etc. ). Once you have these tests set up, any subsequent release or check-in of either RTL or Testbench should be checked with this regression suite.

    If you use regressions efficiently and keep a certain level of discipline then your design and testbench will progress steadily forward. If you do not, you can find that things that used to work no longer work and you will have no valid way to project completion.