In phpunit, is it possible to mock a future callable?

Question

PHPUnit

I have such a class, and in this class a method from another class is called, is it possible to override its result?

class Book {

public function getAuthorName($id)
  {
       $author = Author::model()->findByPk($id);
       return $author->name;
  }
}

I am writing a test

class BookTest{
  public function test()
   {
      $book = new Book();
      // Вот тут как то хочу переопределить возвращаемое значение Author::model()->findByPk($id);
     // Типа при вызове Author::model()->findByPk()->name ==  'Саня';
      $result = $book->getAuthorName(1);
       $this->assertEquals('Саня', result);
   }
}

Or is it unrealistic?