Returns differences by line between the expected output ($wanted) and the actual output ($output). In addition, the value returned from the script can also be tested. The test should be performed outside generate_diff(). If the return value is as expected, pass in FALSE, otherwise pass in an array where the first element is the expected return value and the second is the actual return value.
False if return value was correct, otherwise an array of format:
<?php array( 1, // expected return 2, // actual return value ); ?>