类加载问题PHPUnit测试

Question

我使用以下代码关注Getting Started with PHPUnit：

测试\ MoneyTest.php

<?php

class MoneyTest extends PHPUnit_Framework_TestCase
{
// ...

public function testCanBeNegated()
{
    // Arrange
    $a = new Money(1);

    // Act
    $b = $a->negate();

    // Assert
    $this->assertEquals(-1, $b->getAmount());
}

// ...
}

SRC \ Money.php

 {{{
 <?php
 class Money
{
private $amount;

public function __construct($amount)
{
    $this->amount = $amount;
}

public function getAmount()
{
    return $this->amount;
}

public function negate()
{
    return new Money(-1 * $this->amount);
}

// ...
}

}}}

当我运行phpunit tests/MoneyTest时，我收到以下消息：

PHPUnit 4.8.26 by Sebastian Bergmann and contributors.

E

Time: 56 ms, Memory: 4.00MB

There was 1 error:

1) MoneyTest::testCanBeNegated
Error: Class 'Money' not found

/srv/www/wordpress-default/wp-content/plugins/x-helloworld/tests/MoneyTest.php:10

FAILURES!
Tests: 1, Assertions: 0, Errors: 1.
vagrant@vvv:/srv/www/wordpress-default/wp-content/plugins/x-helloworld$

如何将.. \ src中的类文件识别为测试test \ MoneyTest.php中的引用？

更新

列出版本和操作系统：

php --version
PHP 7.0.8-3+deb.sury.org~trusty+1 (cli) ( NTS )
Copyright (c) 1997-2016 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2016 Zend Technologies
    with Zend OPcache v7.0.8-3+deb.sury.org~trusty+1, Copyright (c) 1999-2016, by Zend Technologies
phpunit --version
PHPUnit 4.8.26 by Sebastian Bergmann and contributors.