11 files declare their use of UserSession in Drupal 8

AccountSwitcherTest.php in core/tests/Drupal/KernelTests/Core/Session/AccountSwitcherTest.php

ContentModerationAccessTest.php in core/modules/content_moderation/tests/src/Kernel/ContentModerationAccessTest.php

Cookie.php in core/modules/user/src/Authentication/Provider/Cookie.php

FormCacheTest.php in core/tests/Drupal/KernelTests/Core/Form/FormCacheTest.php

FunctionalTestSetupTrait.php in core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php

FunctionsTest.php in core/modules/system/tests/src/Kernel/Theme/FunctionsTest.php

InstallerTestBase.php in core/modules/simpletest/src/InstallerTestBase.php

InstallerTestBase.php in core/tests/Drupal/FunctionalTests/Installer/InstallerTestBase.php

RoleAccessCheckTest.php in core/tests/Drupal/Tests/Core/Route/RoleAccessCheckTest.php

SelectProfileFormTest.php in core/tests/Drupal/FunctionalJavascriptTests/Core/Installer/Form/SelectProfileFormTest.php

UserSessionTest.php in core/tests/Drupal/Tests/Core/Session/UserSessionTest.php