diff --git a/core/modules/system/src/Tests/Theme/TwigExtensionTest.php b/core/modules/system/src/Tests/Theme/TwigExtensionTest.php
index 7ca45fb..88acb6b 100644
--- a/core/modules/system/src/Tests/Theme/TwigExtensionTest.php
+++ b/core/modules/system/src/Tests/Theme/TwigExtensionTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Tests\Theme;
 
 use Drupal\simpletest\WebTestBase;
+use Drupal\Component\Render\FormattableMarkup;
 
 /**
  * Tests Twig extensions.
@@ -91,4 +92,14 @@ public function testsRenderZeroValue() {
     $this->assertIdentical($extension->renderVar(0.0), 0, 'TwigExtension::renderVar() renders zero correctly when provided as a double.');
   }
 
+  /**
+   * Tests output of MarkupInterface of TwigExtension->renderVar().
+   */
+  public function testRenderMarkup() {
+    /** @var \Drupal\Core\Template\TwigExtension $extension */
+    $extension = \Drupal::service('twig.extension');
+    $markup = new FormattableMarkup('<span>This is a @markup</span>', ['@markup' => 'MarkupInterface']);
+    $this->assertIdentical($extension->renderVar($markup), $markup, 'TwigExtension::renderVar() returns MarkupInterface correctly.');
+  }
+
 }
diff --git a/core/modules/system/src/Tests/Theme/TwigTransTest.php b/core/modules/system/src/Tests/Theme/TwigTransTest.php
index 7b44496..e35719c 100644
--- a/core/modules/system/src/Tests/Theme/TwigTransTest.php
+++ b/core/modules/system/src/Tests/Theme/TwigTransTest.php
@@ -102,7 +102,6 @@ public function testTwigTransTags() {
   public function testTransRenderArray() {
     $this->drupalGet('twig-theme-test/render-array');
     $this->assertText('This is a trans render array', '{% trans %} with render array value is working correctly.');
-    $this->assertText('This is a MarkupInterface', '{% trans %} with MarkupInterface value is working correctly.');
   }
 
   /**
diff --git a/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.trans_render_array.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.trans_render_array.html.twig
index ed6cb9c..ea04c5d 100644
--- a/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.trans_render_array.html.twig
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig_theme_test.trans_render_array.html.twig
@@ -1,6 +1,3 @@
 {% trans %}
   This is a {{ var }}.
 {% endtrans %}
-{% trans %}
-  {{ markup }}
-{% endtrans %}
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 db0f10e..712b8d7 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
@@ -1,7 +1,5 @@
 <?php
 
-use \Drupal\Component\Render\FormattableMarkup;
-
 /**
  * Implements hook_theme().
  */
@@ -28,7 +26,6 @@ function twig_theme_test_theme($existing, $type, $theme, $path) {
         '#markup' => 'trans render array',
         '#suffix' => '</b>',
       ),
-      'markup' => new FormattableMarkup('<span>This is a @markup</span>', ['@markup' => 'MarkupInterface']),
     ),
     'template' => 'twig_theme_test.trans_render_array',
   );