Writing new or improved tests

• Maybe no one thought what should happen

        # Program to do something sensible

        my $action = something_silly;  # default that will never happen

        if (situation_1)
        {
            $action = something_sensible_1;
        }
        elsif (situation_2)
        {
            $action = something_sensible_2;
        }

        $action->();

• You write a test for situation_3

• No one has even considered that