在 PHPUnit 中测试具有依赖关系的对象

For objects which compose another object as part of their implementation, what's the best way to write the unit test so only the principle object gets tested? Trivial example:

class myObj { 
    public function doSomethingWhichIsLogged()
    {
        // ...
        $logger = new logger('/tmp/log.txt');
        $logger->info('some message');
        // ...
    }
}

我知道可以设计该对象，以便可以注入记录器对象依赖项并因此在单元测试中进行模拟，但情况并非总是如此 - 在更复杂的情况下，您确实需要组合其他对象或进行调用静态方法.

class logger
{
    public function __construct($filepath) {}
    public function info($message) {}
}

class TestMyObj extends PHPUnit_Framework_TestCase 
{
    // ...
}