6 string references to YAML keys in system_test.routing.yml

DrupalMessengerServiceTest::testDrupalMessengerService in core/modules/system/tests/src/Functional/Bootstrap/DrupalMessengerServiceTest.php
Tests Messenger service.
DrupalMessengerServiceTest::testStatusMessageAssertions in core/modules/system/tests/src/Functional/Bootstrap/DrupalMessengerServiceTest.php
Tests assertion methods in WebAssert related to status messages.
KernelTestHttpRequestTest::testRequest in core/tests/Drupal/KernelTests/KernelTestHttpRequestTest.php
Tests making a request.
PageCacheTest::testPageCacheAnonymousRolePermissions in core/modules/page_cache/tests/src/Functional/PageCacheTest.php
Tests the automatic presence of the anonymous role's cache tag.
PageCacheTest::testQueryParameterFormatRequests in core/modules/page_cache/tests/src/Functional/PageCacheTest.php
Tests support for different cache items with different request formats.
RequestSanitizerTest::testRequestSanitizer in core/tests/Drupal/FunctionalTests/HttpKernel/RequestSanitizerTest.php
Tests X-Http-Method-Override header handling.

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