core/lib/Drupal/Core/Template/TwigExtension.php                  | 2 --
 core/modules/system/src/Tests/Theme/EngineTwigTest.php           | 8 ++++++++
 .../modules/twig_theme_test/src/TwigThemeTestController.php      | 9 +++++++++
 .../templates/twig_theme_test.attach_library.html.twig           | 1 +
 .../system/tests/modules/twig_theme_test/twig_theme_test.module  | 4 ++++
 .../tests/modules/twig_theme_test/twig_theme_test.routing.yml    | 7 +++++++
 6 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/core/lib/Drupal/Core/Template/TwigExtension.php b/core/lib/Drupal/Core/Template/TwigExtension.php
index 625aa0e..a2b1f59 100644
--- a/core/lib/Drupal/Core/Template/TwigExtension.php
+++ b/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -286,8 +286,6 @@ public function isUrlGenerationSafe(\Twig_Node $args_node) {
    * {{ attach_library('extension/library_name') }}
    * @endcode
    *
-   * This makes for a much better TX.
-   *
    * @param string $library
    *   An asset library.
    */
diff --git a/core/modules/system/src/Tests/Theme/EngineTwigTest.php b/core/modules/system/src/Tests/Theme/EngineTwigTest.php
index 750ae2e..ff84af7 100644
--- a/core/modules/system/src/Tests/Theme/EngineTwigTest.php
+++ b/core/modules/system/src/Tests/Theme/EngineTwigTest.php
@@ -111,4 +111,12 @@ public function testTwigFileUrls() {
     $this->assertRaw('<div>file_url: ' . $filepath . '</div>');
   }
 
+  /**
+   * Tests the attach of asset libraries.
+   */
+  public function testTwigAttachLibrary() {
+    $this->drupalGet('/twig-theme-test/attach-library');
+    $this->assertRaw('ckeditor.js');
+  }
+
 }
diff --git a/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php b/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
index ff49bd6..50d6c99 100644
--- a/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
+++ b/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
@@ -69,6 +69,15 @@ public function fileUrlRender() {
   }
 
   /**
+   * Renders for testing attach_library functions in a Twig template.
+   */
+  public function attachLibraryRender() {
+    return array(
+      '#theme' => 'twig_theme_test_attach_library',
+    );
+  }
+
+  /**
    * Menu callback for testing the Twig registry loader.
    */
   public function registryLoaderRender() {
diff --git a/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.attach_library.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.attach_library.html.twig
new file mode 100644
index 0000000..0784ab9
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.attach_library.html.twig
@@ -0,0 +1 @@
+{{ attach_library('core/ckeditor') }}
diff --git a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
index 7f6fe35..021d039 100644
--- a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
+++ b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
@@ -50,6 +50,10 @@ function twig_theme_test_theme($existing, $type, $theme, $path) {
     'variables' => array(),
     'template' => 'twig_theme_test.file_url',
   );
+  $items['twig_theme_test_attach_library'] = array(
+    'variables' => array(),
+    'template' => 'twig_theme_test.attach_library',
+  );
   return $items;
 }
 
diff --git a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
index 1001b47..c372c22 100644
--- a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
+++ b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
@@ -40,6 +40,13 @@ twig_theme_test_file_url:
   requirements:
     _access: 'TRUE'
 
+twig_theme_test_attach_library:
+  path: '/twig-theme-test/attach-library'
+  defaults:
+    _controller: '\Drupal\twig_theme_test\TwigThemeTestController::attachLibraryRender'
+  requirements:
+    _access: 'TRUE'
+
 twig_theme_test_registry_loader:
   path: '/twig-theme-test/registry-loader'
   defaults: