Tests should use four-space indentation instead of tabs. The initial indentation level also shouldn't be there.

Furthermore I would suggest doing a comparison between a DateTime and a DateTimeImmutable here too and some more tests in general.

E.g.:

```php
<?php

$iToday = new DateTimeImmutable('today');
$iTomorrow = new DateTimeImmutable('tomorrow');

$mToday = new DateTime('today');
$mTomorrow = new DateTime('tomorrow');

var_dump($iToday < $iTomorrow);
var_dump($iToday == $iTomorrow);
var_dump($iToday > $iTomorrow);

var_dump($iToday == $mToday),
var_dump($iToday === $mToday);

var_dump($iToday < $mTomorrow);
var_dump($iToday == $mTomorrow);
var_dump($iToday > $mTomorrow);

?>
```

With output true, false, false, true, false, true, false, false.