How to apply generics correctly to PHP?

Background

I do have classes (here: ClassA and ClassB) that shall be tested. As these classes are similar, I created an abstract test-class that implements an interface.

Problem

At level 7, PhpStan is unhappy and reports these issues:

• Call to an undefined method object::getId()
• Call to an undefined method object::getName()

I do know that it is unclear which object is calling the methods and thus the issue is reported and I know that the solution is by using GENERICS.

Question

I just started with the use of generics, I have no clue how to solve this correctly.
Anybody so kind to support me here? Thanks!

Code

see PhpStan Playground.

REMARK: The example here is simplified to support the discussion.

<?php

// ---------------------------------------- CLASSES
class ClassA {
    public function getId(): int {
        return 123;
    }
}
class ClassB {
    public function getName(): string {
        return 'abc';
    }
}

// ---------------------------------------- TESTS

/**
 * @template T
 */
interface InterfaceForTest {
    public function getClassName(): string; 
}

/**
 * @template T
 * @implements InterfaceForTest<T>
 */
abstract class AbstractClassTest implements InterfaceForTest {
    public function createObject(): object
    {
        $class  = $this->getClassName();
        $object = new $class();
        return $object;
    }
}

/**
 * @template T
 * @extends AbstractClassTest<T>
 */
class ClassATest extends AbstractClassTest {
    public function getClassName(): string
    {
        return ClassA::class;
    }

    public function testA(): void
    {
        $obj = $this->createObject();

        assert($obj->getId() === 123);      // makes PHPStan unhappy at level 7
    }
}

/**
 * @template T
 * @extends AbstractClassTest<T>
 */
class ClassBTest extends AbstractClassTest {
    public function getClassName(): string
    {
        return ClassB::class;
    }

    public function testA(): void
    {
        $obj = $this->createObject();
        
        assert($obj->getName() === 'abc');  // makes PHPStan unhappy at level 7
    }
}