Add test coverage to ensure KernelTestBase's simulated current Request has a hostname

Moving to a minor as its been many years.

As mentioned in #14 since the parent issue landed would it be worth adding this additional assertion or not needed?

I don't see a bug here, changing to a task. The priority to set an issue to is defined on Issue Priority field → (which does not refer to the number of years). As an example there is a Critical issue that is now 16 years old.

A parent issue is not mentioned in #14. What is the parent issue being referred to here?

This is retesting the patch on an unsupported version of Drupal instead of a supported version.

Arguably this code would be better in testSetUp() where we already check the path:

    $request = $this->container->get('request_stack')->getCurrentRequest();
    $this->assertNotEmpty($request);
    $this->assertEquals('/', $request->getPathInfo());

I was trying to understand where this is actually set up. run-tests.sh explicitly sets it:

  $_SERVER['SERVER_NAME'] = 'localhost';

but if I bypass this and run tests directly via PHPUnit, the test still passes. I think this is just because Symfony's Request::create() method does this:

        $server = array_replace([
            'SERVER_NAME' => 'localhost',

I suppose this is still worth adding a test for if we have expectations on it elsewhere.