I have such as Testcase:

class GenerateTest extends AbstractTestCase
{
    private int $requestTime = 0;

    ...

    protected function setUp(): void
    {
        $this->requestTime = $_SERVER['REQUEST_TIME']; // this is not null, verified by var_dump()
        parent::setUp();
    }

    protected function tearDown(): void
    {
        parent::tearDown();

        $_SERVER['REQUEST_TIME'] = $this->requestTime;
    }

I am getting the error

Cannot assign null to property GenerateTest::$requestTime of type int"

without a line number.

Even if I comment the lines in setup/teardown, I get the error. In the class are no further assignments to requestTime.

Where does this come from?

If i use ?int it works, but I want to understand the root cause.

Does PHPUnit “automagically” reset class variables?