12 files declare their use of MemoryBackend in Drupal 10

AssetResolverTest.php in core/tests/Drupal/Tests/Core/Asset/AssetResolverTest.php

Contains \Drupal\Tests\Core\Asset\AssetResolverTest.

BackendChainImplementationUnitTest.php in core/tests/Drupal/Tests/Core/Cache/BackendChainImplementationUnitTest.php

BackendChainTest.php in core/tests/Drupal/KernelTests/Core/Cache/BackendChainTest.php

ChainedFastBackendTest.php in core/tests/Drupal/Tests/Core/Cache/ChainedFastBackendTest.php

MemoryBackendTest.php in core/tests/Drupal/KernelTests/Core/Cache/MemoryBackendTest.php

MemoryCache.php in core/lib/Drupal/Core/Cache/MemoryCache/MemoryCache.php

PluginTestBase.php in core/tests/Drupal/KernelTests/Core/Plugin/PluginTestBase.php

RendererBubblingTest.php in core/tests/Drupal/Tests/Core/Render/RendererBubblingTest.php

Contains \Drupal\Tests\Core\Render\RendererBubblingTest.

RendererTestBase.php in core/tests/Drupal/Tests/Core/Render/RendererTestBase.php

Contains \Drupal\Tests\Core\Render\RendererTestBase.

RouteProviderTest.php in core/tests/Drupal/KernelTests/Core/Routing/RouteProviderTest.php

Contains \Drupal\KernelTests\Core\Routing\RouteProviderTest.

StorageComparer.php in core/lib/Drupal/Core/Config/StorageComparer.php

ThemeExtensionListTest.php in core/tests/Drupal/Tests/Core/Extension/ThemeExtensionListTest.php