InvocationMocker expects method not found PHPUnit

When I wanted to servicetest my method in Laravel 5.5 I wanted to use the expects method. I have used it in another project (It was in the KernelTestCase class there) that did not use laravel and it worked there. Here I can't find where it is or what package I need to add to make it work.

Does anyone know what package I need for it to work or which class to extend?

Thanks in advance.