The optional extra homework is functional testing of the chess clock that you have modelled for your mandatory home assignment.
You have to write test cases (Scenario), which define sequences of inputs (pushing buttons), or sometimes even time settings, and expected outputs (display contents, peep tons) for your chess clock. At the end of each test case (and whenever meaningful, even within the sequences) the outputs must be checked. The test cases have to run successfully on your chess clock, at the end. Read more »