So the problem is that the test runner has to compute the expected results every time she runs the test script.
A slight improvement will be to show the expected results next to the actual values.
<?php require_once(dirname(__FILE__) . '/../includes/mylib.php'); print add(1,1) . ' == 2<br>'; print add(2,2) . ' == 4<br>'; print add(1,1,1) . ' == 3<br>'; ?>
2 == 2 4 == 4 2 == 3
This is still hard to follow when there are lots of cases or even a few cases with large output but it seems to be a step in the good direction.