Solution Review: Dependency Injection

<?php 
class Article { 
    protected $title; 
    protected $author;
    public function __construct($title, $author) {
        $this -> title = $title;
        $this -> author = $author;
    }
    
    public function getTitle() {
        return $this -> title; 
    }
    public function getAuthor() {
        return $this -> author; 
    }
}
class Author { 
    protected $name;
    
    public function setName($name) {
        $this -> name = $name;
    }
    public function getName() {
        return $this -> name; 
    }
}
function test()
{
  $author1 = new Author(); 
  $author1 -> setName("Joe");
  $title = "To PHP and Beyond";
  $article1 = new Article($title,$author1);
  return $article1 -> getTitle() . ' by ' . $article1 -> getAuthor() -> getName();
}
echo test();
?>