Symfony 4 phpunit : KERNEL_CLASS env variable error

I'm trying to learn how to make phpunit by testing the User class made by "make:user" but i'm facing this problem when extending "KernelTestCase" and run the test :

LogicException: You must set the KERNEL_CLASS environment variable to the fully-qualified class name of your Kernel in phpunit.xml / phpunit.xml.dist or override the "App\tests\Entity
UsersTest::createKernel()" or "App\tests\Entity\UsersTest::getKernelClass()" method.

Here is my test, i'm trying to test an Entity :

I'm trying to fix it since 2 days with my friend Google but I didn't found any solution. Can you help me ? Thank you guys !