diff --git a/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageThemeFunctionsTest.php b/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageThemeFunctionsTest.php
index f0c671d..ab66ee3 100644
--- a/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageThemeFunctionsTest.php
+++ b/core/modules/responsive_image/lib/Drupal/responsive_image/Tests/ResponsiveImageThemeFunctionsTest.php
@@ -54,13 +54,13 @@ function testResponsiveImageTheme() {
     );
     $rendered_element = render($element);
     $expected_result = '<picture><source src="'.$url.'" /><noscript><img class="image-style-test" src="' . $url . '" /></noscript></picture>';
-    $this->assertTrue(strpos($rendered_element, $expected_result) !== FALSE, 'img element in template_preprocess_responsive_image() correctly renders the alt option.');
+    $this->assertEqual($rendered_element, $expected_result, 'img1 element in template_preprocess_responsive_image() correctly renders the alt option.');
 
     // Test using template_preprocess_responsive_image() without passing a value for the alt option.
     unset($element['#alt']);
     $rendered_element = render($element);
     $expected_result = '<picture><source src="'.$url.'" /><noscript><img class="image-style-test" src="' . $url . '" alt="" /></noscript></picture>';
-    $this->assertTrue(strpos($rendered_element, $expected_result) !== FALSE, 'img element in template_preprocess_responsive_image() correctly renders the alt option.');
+    $this->assertEqual($rendered_element, $expected_result, 'img element in template_preprocess_responsive_image() correctly renders the alt option.');
   }
 
     /**