There's a current failure in the mod/assign/tests/behat/relative_dates.feature file.

The intention was to have an assignment valid for one month and a user (student 2) who started on the first day of the current month and who would have access to this assignment. Howeverm because the 'valid for one month' steps were using 'first and last days of -2 months' syntax, the number of days could vary. Thus, we ended up in a situation on August 30 (today) where the -2 months start and end (for June) gives an assignment valid for only 30 days. Which means it expires on August 30 for the student starting in August - about 5 seconds before the student logs in during the behat test.

Solution:

Change all the ranges to be so large that we don't hit these 'number of days in a month' type problems.