BUG Fix race conditions in DatetimeFieldTest

tests/php/Forms/DatetimeFieldTest.php

@@ -23,11 +23,14 @@ class DatetimeFieldTest extends SapphireTest
     {
         parent::setUp();
         i18n::set_locale('en_NZ');
+        // Fix now to prevent race conditions
+        DBDatetime::set_mock_now('2010-04-04');
         $this->timezone = date_default_timezone_get();
     }
 
     protected function tearDown()
     {
+        DBDatetime::clear_mock_now();
         date_default_timezone_set($this->timezone);
         parent::tearDown(); // TODO: Change the autogenerated stub
     }