I am seeing failures during the unit tests:

PHP Fatal error: Maximum execution time of 300 seconds exceeded in C:\Users\tjh238\workspace\moodle_head\lib\moodlelib.php on line 10745

As far as I can work out, what is going on is this:

1. Some code somewhere calls set_time_limit supposedly to avoid time-outs.
2. If the tests run fast enough, then there is no problem, but if your computer is slow, then some time later the tests time-out on an unrelated test.

I think we should add code to reset_all_data to detect changes in max_execution_time, and report them as errors.