Quote these dates to prevent intermittent test failure. Suppose local time is 00:50 GMT+1. Without the quoting, the YAML parser would parse this as 00:50 UTC, into the local time of 01:50 GMT+1. Then, it would get written into the database in local time as 01:50. When it came back out the UTC date from the database and the UTC date of two weeks ago would be compared. The former would be 23:50, and the latter would be 00:50, so the two dates would differ, causing the assertion to fail. Quoting it prevents the YAML parser from getting involved.