最后面单元测试运行的一个问题

IteratorTest.php

//...
foreach ($bookList as $book) {
    $books[] = $book->getAuthorAndTitle();
}
$this->assertEquals(
    [
        'Learning PHP Design Patterns by William Sanders',
        'Professional Php Design Patterns by Aaron Saray',
        'Clean Code by Robert C. Martin',
    ],  
    $books
);

这里运行单元测试得到的是

1) DesignPatterns\Behavioral\Iterator\IteratorTest::testCanIterateOverBookList
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
-    0 => 'Learning PHP Design Patterns ...anders'
-    1 => 'Professional Php Design Patte... Saray'
-    2 => 'Clean Code by Robert C. Martin'

foreach 是遍历 $bookList 的私有变量 $books，应该提供一个方法获取这个私有变量吧？

class BookList implements \Countable, \Iterator
{
    //...
    public function getBooks(): array
    {
        return $this->books;
    }
}

然后单元测试的代码应该是

foreach ($bookList->getBooks() as $book) {
    $books[] = $book->getAuthorAndTitle();
}