diff --git a/core/lib/Drupal/Core/Template/TwigNodeTrans.php b/core/lib/Drupal/Core/Template/TwigNodeTrans.php
index 64e0b2e..13677cc 100644
--- a/core/lib/Drupal/Core/Template/TwigNodeTrans.php
+++ b/core/lib/Drupal/Core/Template/TwigNodeTrans.php
@@ -11,8 +11,7 @@
 namespace Drupal\Core\Template;

 /**
- * The 'trans' tag allows the content string to be passed to the translation
- * system for internationalization.
+ * A class that defines the Twig 'trans' tag for Drupal.
  */
 class TwigNodeTrans extends \Twig_Node {

diff --git a/core/lib/Drupal/Core/Template/TwigTransTokenParser.php b/core/lib/Drupal/Core/Template/TwigTransTokenParser.php
index e1f4807..44f6d21 100644
--- a/core/lib/Drupal/Core/Template/TwigTransTokenParser.php
+++ b/core/lib/Drupal/Core/Template/TwigTransTokenParser.php
@@ -20,6 +20,7 @@
  * @see \Twig_TokenParser
  */
 class TwigTransTokenParser extends \Twig_TokenParser {
+
   /**
    * {@inheritdoc}
    */
@@ -79,6 +80,8 @@ public function getTag() {
    *   The expression to check.
    * @param integer $lineno
    *   The source line.
+   *
+   * @throws \Twig_Error_Syntax
    */
   protected function checkTransString(\Twig_NodeInterface $body, $lineno) {
     foreach ($body as $node) {
diff --git a/core/modules/system/lib/Drupal/system/Tests/Theme/TwigTransTest.php b/core/modules/system/lib/Drupal/system/Tests/Theme/TwigTransTest.php
index 8717147..8c984f0 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Theme/TwigTransTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Theme/TwigTransTest.php
@@ -71,14 +71,6 @@ protected function setUp() {
     theme_enable(array('test_theme'));
     \Drupal::config('system.theme')->set('default', 'test_theme')->save();

-    // Enable twig debug and write to the test settings.php file.
-    $this->settingsSet('twig_debug', TRUE);
-    $settings['settings']['twig_debug'] = (object) array(
-      'value' => TRUE,
-      'required' => TRUE,
-    );
-    $this->writeSettings($settings);
-
     // Create and log in as admin.
     $this->admin_user = $this->drupalCreateUser(array(
       'administer languages',
@@ -108,7 +100,7 @@ protected function setUp() {

     // Assign lolspeak to be the default language.
     $edit = array('site_default_language' => $this->langcode);
-    $this->drupalpost('admin/config/regional/settings', $edit, t('Save configuration'));
+    $this->drupalPost('admin/config/regional/settings', $edit, t('Save configuration'));

     // Reset the static cache of the language list.
     drupal_static_reset('language_list');
@@ -144,49 +136,64 @@ public function testTwigTransTags() {
     );

     $this->assertRaw(
-      '<!-- TRANSLATION: "Hello star.", PLURAL: "Hello @count stars." -->',
-      'The "twig_debug" translation comment markup printed successfully for the above test.'
-    );
-
-    $this->assertRaw(
       'ESCAPEE: &amp;&quot;&lt;&gt;',
       '{{ token }} was successfully translated and prefixed with "@".'
     );

     $this->assertRaw(
-      '<!-- TRANSLATION: "Escaped: @string" -->',
-      'The "twig_debug" translation comment markup printed successfully for the above test.'
-    );
-
-    $this->assertRaw(
       'PAS-THRU: &"<>',
       '{{ token|passthrough }} was successfully translated and prefixed with "!".'
     );

     $this->assertRaw(
-      '<!-- TRANSLATION: "Pass-through: !string" -->',
-      'The "twig_debug" translation comment markup printed successfully for the above test.'
-    );
-
-    $this->assertRaw(
       'PLAYSHOLDR: <em class="placeholder">&amp;&quot;&lt;&gt;</em>',
       '{{ token|placeholder }} was successfully translated and prefixed with "%".'
     );

     $this->assertRaw(
-      '<!-- TRANSLATION: "Placeholder: %string" -->',
-      'The "twig_debug" translation comment markup printed successfully for the above test.'
-    );
-
-    $this->assertRaw(
       'DIS complex token HAZ LENGTH OV: 3. IT CONTAYNZ: <em class="placeholder">12345</em> AN &amp;&quot;&lt;&gt;. LETS PAS TEH BAD TEXT THRU: &"<>.',
       '{{ complex.tokens }} were successfully translated with appropriate prefixes.'
     );

-    $this->assertRaw(
-      '<!-- TRANSLATION: "This @name has a length of: @count. It contains: %numbers and @bad_text. Lets pass the bad text through: !bad_text." -->',
-      'The "twig_debug" translation comment markup printed successfully for the above test.'
+    // Ensure debug output does not print.
+    $this->checkDebugVisible(FALSE);
+  }
+
+  /**
+   * Test Twig "trans" debug markup.
+   */
+  public function testTwigTransDebug() {
+    // Enable twig debug and write to the test settings.php file.
+    $this->settingsSet('twig_debug', TRUE);
+    $settings['settings']['twig_debug'] = (object) array(
+      'value' => TRUE,
+      'required' => TRUE,
+    );
+    $this->writeSettings($settings);
+
+    // Get page for assertion testing.
+    $this->drupalGet('twig-theme-test/trans', array('language' => language_load('xx')));
+
+    // Ensure debug output is printed.
+    $this->checkDebugVisible(TRUE);
+  }
+
+  protected function checkDebugVisible($visible) {
+    $tests = array(
+      '{% trans %} with {% plural %}' => '<!-- TRANSLATION: "Hello star.", PLURAL: "Hello @count stars." -->',
+      '{{ token }}' => '<!-- TRANSLATION: "Escaped: @string" -->',
+      '{{ token|passthrough }}' => '<!-- TRANSLATION: "Pass-through: !string" -->',
+      '{{ token|placeholder }}' => '<!-- TRANSLATION: "Placeholder: %string" -->',
+      '{{ complex.tokens }}' => '<!-- TRANSLATION: "This @name has a length of: @count. It contains: %numbers and @bad_text. Lets pass the bad text through: !bad_text." -->',
     );
+    foreach ($tests as $test => $markup) {
+      if ($visible) {
+        $this->assertRaw($markup, "Twig debug translation markup exists in source for: $test");
+      }
+      else {
+        $this->assertNoRaw($markup, "Twig debug translation markup does not exist in source for: $test");
+      }
+    }
   }

   /**
@@ -194,9 +201,9 @@ public function testTwigTransTags() {
    *
    * Borrowed from \Drupal\locale\Tests\LocaleImportFunctionalTest.
    *
-   * @param $contents
+   * @param string $contents
    *   Contents of the .po file to import.
-   * @param $options
+   * @param array $options
    *   Additional options to pass to the translation import form.
    */
   protected function importPoFile($contents, array $options = array()) {