phpunit还没有在Archlinux的仓库中，可以采用下载安装方式：
错误：
PHP Warning: realpath(): open_basedir restriction in effect. File(/usr/local/bin/phpunit) is not within the allowed path(s): (/srv/http/:/home/:/tmp/:/usr/share/pear/) in /usr/local/bin/phpunit on line 3
PHP Fatal error: Class 'Phar' not found in /usr/local/bin/phpunit on line 714
启用phar扩展：
先解决Fatal error: Class 'Phar' not found。
ls /usr/lib/php/modules
发现有 phar.so，说明Phar的扩展已经安装，那么是不是该扩展没有Enable呢？
打开 /etc/php/php.ini搜索 phar，果然发现 extension=phar.so被注释掉了。去掉该行前面的 ;，保存php.ini，再次运行 phpunit --version。
PHP Warning: realpath(): open_basedir restriction in effect. File(/usr/local/bin/phpunit) is not within the allowed path(s): (/srv/http/:/home/:/tmp/:/usr/share/pear/) in /usr/local/bin/phpunit on line 3
PHP Warning: Phar::mapPhar(): open_basedir restriction in effect. File(/usr/local/bin/phpunit) is not within the allowed path(s): (/srv/http/:/home/:/tmp/:/usr/share/pear/) in /usr/local/bin/phpunit on line 714
Fatal error解决了，但警告还在，而且phpunit没有正常运行。
php对文件访问的保护机制
google之，发现这里有解释: http://www.templatemonster.com/help/open_basedir-restriction-in-effect-filex-is-not-within-the-allowed-paths-y.html
PHP open_basedir protection tweak is a Safe Mode security measure that prevents users from opening files or scripts located outside of their home directory with PHP, unless the folder has specifically excluded. PHP open_basedir setting if enabled, will ensure that all file operations to be limited to files under certain directory, and thus prevent php scripts for a particular user from accessing files in unauthorized user’s account. When a script tries to open a file with, for example, fopen() or gzopen(), the location of the file is checked. When the file is outside the specified or permissible directory-tree, PHP will refuse to open it and the following errors may occur: ...
翻译：
php.ini中的open_basedir是php为保证安全进行文件访问的设置。
如果该选项被赋值，所有的文件操作将限定在特定的目录里，这样可以防止某个用户使用php脚本读取未授权的内容。
当你想通过fopen或gzopen打开一个文件时，如果该文件的位置不再被允许的目录下面，就会出现上述的警告信息。
从警告信息可见：访问的目录包括 /srv/http/:/home/:/tmp/:/usr/share/pear/，刚好 ~/bin即在PATH变量中，也属于可以被php脚本读取的目录，于是：
再运行phpunit --version，得到正确结果：
PHPUnit 4.5.0 by Sebastian Bergmann and contributors.
phpunit安装成功。