PHPUnit Composer autoload?

Question

Yii

I have a yii2 project. Yes, I know there by default codeception, I tried to figure it out - but for me it's TOO COMPLEX! I only need unit tests, and there is a lot of stuff there. In general, I sawed codeception and sawed phpunit. It basically works (a simple demo of assertTrue without dependencies is wound up), but when I try to use my classes from the project, everything collapses "class not found". I'm pretty sure it's a startup problem. For some reason it doesn't work with phpunit. How to be? Googled, tried to put autoload in composer.json, specify phpunit --bootstrap vendor/autoload.php as it is written in Google, but nothing worked. How can I start tests? I really need them right now!
PS php 5.6, phpunit 5, yii 2.0.14