Do you mean to say this can't be done in PHP?

Because the fact that it's available in PHP tells us that it has been implemented in PHP, there are pre-determined and random unit tests in PHP, and that those have been completed.

In PHP, the Node class is more or less:

final class Node {
  // ... some irrelevant fields
  public function getNext(): Node {
    return some_node_following_the_current_one;
  }
  
  // ... some irrelevant implementation details
}

All what is needed to oslve the kata is to know that class is named Node and that it has the method Node nextNode(). I will see how to make this clearer.

just skip this if you're doing PHP, it makes no sense and it's just garbage

it is not provided by the Kata for PHP. no idea what Node is