diff --git a/core/modules/system/src/Tests/Theme/TwigLoaderTest.php b/core/modules/system/src/Tests/Theme/TwigLoaderTest.php
new file mode 100644
index 0000000..e75184f
--- /dev/null
+++ b/core/modules/system/src/Tests/Theme/TwigLoaderTest.php
@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Theme\TwigLoaderTest.
+ */
+
+namespace Drupal\system\Tests\Theme;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests adding Twig loaders.
+ *
+ * @group Theme
+ */
+class TwigLoaderTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = ['twig_loader_test'];
+
+}
diff --git a/core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php b/core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php
new file mode 100644
index 0000000..09ec118
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php
@@ -0,0 +1,45 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\twig_loader_test\Loader\TestLoader.
+ */
+
+namespace Drupal\twig_loader_test\Loader;
+
+use Drupal\Core\Template\Loader;
+
+/**
+ * A test Twig loader.
+ */
+class TestExtension implements Twig_LoaderInterface, Twig_ExistsLoaderInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getSource($name) {
+    return $name;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function exists($name) {
+    return TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheKey($name) {
+    return $name;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isFresh($name, $time) {
+    return TRUE;
+  }
+
+}
diff --git a/core/modules/system/tests/modules/twig_loader_test/twig_extension_test.services.yml b/core/modules/system/tests/modules/twig_loader_test/twig_extension_test.services.yml
new file mode 100644
index 0000000..1b19948
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_loader_test/twig_extension_test.services.yml
@@ -0,0 +1,5 @@
+services:
+  twig_loader_test.twig.test_loader:
+    class: Drupal\twig_loader_test\Loader\TestLoader
+    tags:
+      - { name: twig.loader }
diff --git a/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.info.yml b/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.info.yml
new file mode 100644
index 0000000..cf04aae
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.info.yml
@@ -0,0 +1,6 @@
+name: 'Twig Loader Test'
+type: module
+description: 'Support module for testing adding Twig loaders.'
+package: Testing
+version: VERSION
+core: 8.x