8 files declare their use of FailureMarker

ApiController.php in core/modules/package_manager/tests/modules/package_manager_test_api/src/ApiController.php
FailureMarkerRequirementTest.php in core/modules/package_manager/tests/src/Functional/FailureMarkerRequirementTest.php
FailureMarkerTest.php in core/modules/package_manager/tests/src/Kernel/FailureMarkerTest.php
PackageManagerKernelTestBase.php in core/modules/package_manager/tests/src/Kernel/PackageManagerKernelTestBase.php
PackageManagerRequirements.php in core/modules/package_manager/src/Install/Requirements/PackageManagerRequirements.php
PackageManagerRequirementsHooks.php in core/modules/package_manager/src/Hook/PackageManagerRequirementsHooks.php
SandboxManagerBaseTest.php in core/modules/package_manager/tests/src/Kernel/SandboxManagerBaseTest.php
StageCommitExceptionTest.php in core/modules/package_manager/tests/src/Kernel/StageCommitExceptionTest.php

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