function assertDateTimeEqual($date_time1, $date_time2, $delta = 1, $msg = null)
 {
     $ts1 = (new SimpleDateTime($date_time1))->gmtTimestamp();
     $ts2 = (new SimpleDateTime($date_time2))->gmtTimestamp();
     if (!$delta instanceof SimpleTimeInterval) {
         $delta = new SimpleTimeInterval($delta);
     }
     $diff = new SimpleTimeInterval(abs($ts1 - $ts2));
     $test = $diff->seconds() <= $delta->seconds();
     if (is_null($msg) && !$test) {
         $diff_str = self::build_time_interval_string($diff);
         $delta_str = self::build_time_interval_string($delta);
         $msg = "Timestamps should be equal, but differ by {$diff_str} >= " . "{$delta_str} seconds.";
     }
     $this->assertTrue($test, $msg);
 }