I saw this (only once) when running tests on latest master on Windows 7:

<pre>
2) core_moodlelib_testcase::test_complete_user_login
Time is lower that allowed start value
Failed asserting that '1396532431' is equal to 1396532432 or is greater than 1396532432.

C:\Users\sm449\workspace\core-moodle-github\lib\phpunit\classes\advanced_testcase.php:396
C:\Users\sm449\workspace\core-moodle-github\lib\tests\moodlelib_test.php:2467
C:\Users\sm449\workspace\core-moodle-github\lib\phpunit\classes\advanced_testcase.php:80

To re-run:
c:/users/sm449/workspace/core-moodle-github/vendor/phpunit/phpunit/composer/bin/phpunit core_moodlelib_testcase C:\Users\sm449\workspace\core-moodle-github\lib\tests\moodlelib_test.php
</pre>

Looks like a rare time error, sorry I didn't have time to code a fix just now, but thought I'd report it at least.