TypeError: strcasecmp() error when running tests on core/modules/system/tests/src/Functional/Routing/RouterTest.php

Problem/Motivation

I was running some tests in a Drupal 11.0.10 instance (DDEV, PHP 8.3):

$ ./vendor/bin/phpunit -c web/core/phpunit.xml ./web/core/modules/system/tests/src/Functional/Routing/RouterTest.php

and I am hitting this error:

daniel@drupal:/var/www/html$ ./vendor/bin/phpunit -c web/core/phpunit.xml ./web/core/modules/system/tests/src/Functional/Routing/RouterTest.php
PHPUnit 10.5.45 by Sebastian Bergmann and contributors.

Runtime:       PHP 8.3.14
Configuration: /var/www/html/web/core/phpunit.xml

E.............                                                    14 / 14 (100%)

HTML output was generated.
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-255-28550090.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-256-10338684.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-257-10338684.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-258-10338684.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-259-10338684.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-260-49606092.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-261-49606092.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-262-45676727.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-263-76088657.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-264-24547444.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-265-12070873.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-266-43380184.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-267-43380184.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-268-43380184.html

....

dev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-274-43380184.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-275-43380184.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-276-43380184.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-277-43380184.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-278-33436292.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-279-79848419.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-280-79848419.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-281-79848419.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-282-79848419.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-283-24906904.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-284-69988493.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-285-69988493.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-286-69988493.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-287-69988493.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-288-69988493.html
http://drupal.11.0.10.ddev.site/sites/simpletest/browser_output/Drupal_Tests_system_Functional_Routing_RouterTest-289-69988493.html


Time: 00:45.135, Memory: 6.00 MB

There was 1 error:

1) Drupal\Tests\system\Functional\Routing\RouterTest::testFinishResponseSubscriber

TypeError: strcasecmp(): Argument #1 ($string1) must be of type string, null given

/var/www/html/web/core/modules/system/tests/src/Functional/Routing/RouterTest.php:49

ERRORS!
Tests: 14, Assertions: 75, Errors: 1.

Screenshot:

Steps to reproduce

1. Install latest Drupal 11 release, or make sure your current D11 has phpunit installed.
2. From the directory where the ./vendor directory is located, run:

./vendor/bin/phpunit -c web/core/phpunit.xml ./web/core/modules/system/tests/src/Functional/Routing/RouterTest.php

You'll see the error mentioned above

Proposed resolution

If you take a look at this snippet from RouterTest.php (lines 49-51):

    if (strcasecmp($session->getResponseHeader('vary'), 'accept-encoding') !== 0) {
      $this->assertSession()->responseHeaderDoesNotExist('Vary');
    }

You can add a small validation to check if $session->getResponseHeader('vary') is empty or not before calling strcasecmp(), something like this:

    if (strcasecmp($session->getResponseHeader('vary') ?? "", 'accept-encoding') !== 0) {
      $this->assertSession()->responseHeaderDoesNotExist('Vary');
    }

After that the tests passed:

But the main question is: Are the tests expecting the Vary header from FinishResponseSubscriber to have a value? I am not sure about that.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet