Laravel base_path（）在加载的类中未定义

I've autoloaded a helper class using composer.json through:

"autoload": {
    "classmap": [
     ...
    ],
    "files": ["app/library/test.class.php"]

However when using (any) laravel package along, base_path() and other helper functions are undefined. Are they being loaded before vendors ? or what is the issue here?

I want to use Laravel helper functions in this class.