for my $delta ($delta_time, $delta_date){
# the above are likely to be Date::Manip[::*] objects - which ones????
    for my $field (qw (seconds minutes hours days months years)) {
    for my $type ('','total_') {
        my $func = "${type}${field}";
        # this is the method name to be called via the $delta objects
        for my $prec ('','trunc') {
            # this is the a parameter to above method, one is empty one is 'trunc'
            diag ("comapring ".$delta->$func($prec)." to ".$test_values[$test_index]." at ".$test_index." func=".$func." prec=".$prec." type=".$type." field=".$field);
         ok($delta->$func($prec) == $test_values[$test_index++],"$func($prec) ($delta_text[$delta_index])")
         # it calls e.g. this: $delta->total_seconds('trunc')
         # and it compares the returned result with an item from an array
         # of expected results $test_values[$test_index]