I'd probably go with something like this

while(!$graduated)
{
        $day++;
        if($test[$day]) { &write_test }
        &party;
}

sub write_test
{
        if(int rand 100 > 90) {
                print "Test passed\n";
        } else {
                print "Test failed\n";
        }
}
[download]

The party subroutine is way to complex to submit here..