diff -u b/core/modules/system/src/Tests/Theme/TwigTransTest.php b/core/modules/system/src/Tests/Theme/TwigTransTest.php
--- b/core/modules/system/src/Tests/Theme/TwigTransTest.php
+++ b/core/modules/system/src/Tests/Theme/TwigTransTest.php
@@ -83,8 +83,26 @@
    * Test Twig "trans" tags.
    */
   public function testTwigTransTags() {
+    // Run this once without and once with Twig debug because trans can work
+    // differently depending on that setting.
     $this->drupalGet('twig-theme-test/trans', array('language' => \Drupal::languageManager()->getLanguage('xx')));
+    $this->assertTwigTransTags();
 
+    // Enable debug, rebuild the service container, and clear all caches.
+    $parameters = $this->container->getParameter('twig.config');
+    $parameters['debug'] = TRUE;
+    $this->setContainerParameter('twig.config', $parameters);
+    $this->rebuildContainer();
+    $this->resetAll();
+
+    $this->drupalGet('twig-theme-test/trans', array('language' => \Drupal::languageManager()->getLanguage('xx')));
+    $this->assertTwigTransTags();
+  }
+
+  /**
+   * Asserts Twig trans tags.
+   */
+  protected function assertTwigTransTags() {
     $this->assertText(
       'OH HAI SUNZ',
       '{% trans "Hello sun." %} was successfully translated.'
@@ -156,25 +174,7 @@
     );
     // Makes sure https://www.drupal.org/node/2489024 doesn't happen without
     // twig debug.
-    $this->assertText(
-      "Hello kittens - ' . print('I am bad code!') . '",
-      'Running php code inside a Twig trans is not possible.'
-    );
-  }
-
-  /**
-   * Test Twig "trans" debug markup.
-   */
-  public function testTwigTransDebug() {
-    // Enable debug, rebuild the service container, and clear all caches.
-    $parameters = $this->container->getParameter('twig.config');
-    $parameters['debug'] = TRUE;
-    $this->setContainerParameter('twig.config', $parameters);
-    $this->rebuildContainer();
-    $this->resetAll();
-
-    // Get page for assertion testing.
-    $this->drupalGet('twig-theme-test/trans', array('language' => \Drupal::languageManager()->getLanguage('xx')));
+    $this->assertNoText(pi(), 'Running php code inside a Twig trans is not possible.');
   }
 
   /**
diff -u b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.trans.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.trans.html.twig
--- b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.trans.html.twig
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.trans.html.twig
@@ -99,5 +99,5 @@
 <div>
   {% trans %}
-    Hello kittens - ' . print('I am bad code!') . '
+    Number I never remember: ' . print(pi()) . '
   {% endtrans %}
 </div>