Path coverage

There are classes of errors which branch coverage cannot detect:

        $h = 0;
        if ($x)
        {
            $h = { a => 1 };
        }
        if ($y)
        {
            print $h->{a};
        }

• 100% branch coverage with ($x, $y) set to (1, 1) and (0, 0)

• (0, 1) => BOOM