diff -u b/core/lib/Drupal/Component/Assertion/Handle.php b/core/lib/Drupal/Component/Assertion/Handle.php
--- b/core/lib/Drupal/Component/Assertion/Handle.php
+++ b/core/lib/Drupal/Component/Assertion/Handle.php
@@ -5,62 +5,71 @@
+ *
+ * For PHP 5 this contains \AssertionError as well.
  */
 
-// Force the AssertionError class to exist at the root namespace for PHP 5.
-// This class exists natively in PHP 7. Note that in PHP 7 it extends from
-// Error, not Exception, but that isn't possible for PHP 5 - all exceptions
-// must extend from exception.
 namespace {
-  if (!class_exists('AssertionError', FALSE)) {
+
+if (!class_exists('AssertionError', FALSE)) {
+
+  /**
+   * Emulates PHP 7 AssertionError as closely as possible.
+   *
+   * We force this class to exist at the root namespace for PHP 5.
+   * This class exists natively in PHP 7. Note that in PHP 7 it extends from
+   * Error, not Exception, but that isn't possible for PHP 5 - all exceptions
+   * must extend from exception.
+   */
+  class AssertionError extends Exception {
+
     /**
-     * Emulates PHP 7 AssertionError as closely as possible.
+     * {@inheritdoc}
      */
-    class AssertionError extends Exception {
-      /**
-       * {@inheritdoc}
-       */
-      public function __construct($message = '', $code = 0, Exception $previous = NULL, $file = '', $line = 0) {
-        parent::__construct($message, $code, $previous);
-        // Preserve the filename and line number of the assertion failure.
-        $this->file = $file;
-        $this->line = $line;
-      }
-
+    public function __construct($message = '', $code = 0, Exception $previous = NULL, $file = '', $line = 0) {
+      parent::__construct($message, $code, $previous);
+      // Preserve the filename and line number of the assertion failure.
+      $this->file = $file;
+      $this->line = $line;
     }
+
   }
 }
 
+}
+
 namespace Drupal\Component\Assertion {
+
+/**
+ * Handler for runtime assertion failures.
+ *
+ * This class allows PHP 5.x to throw exceptions on runtime assertion fails
+ * in the same manner as PHP 7, and sets the ASSERT_EXCEPTION flag to TRUE
+ * for the PHP 7 runtime.
+ *
+ * @ingroup php_assert
+ */
+class Handle {
+
   /**
-   * Handler for runtime assertion failures.
-   *
-   * This class allows PHP 5.x to throw exceptions on runtime assertion fails
-   * in the same manner as PHP 7, and sets the ASSERT_EXCEPTION flag to TRUE
-   * for the PHP 7 runtime.
-   *
-   * @ingroup php_assert
+   * Registers uniform assertion handling.
    */
-  class Handle {
-    /**
-     * Registers uniform assertion handling.
-     */
-    public static function register() {
-      // Since we're using exceptions, turn error warnings off.
-      assert_options(ASSERT_WARNING, FALSE);
-
-      if (version_compare(PHP_VERSION, '7.0.0-dev') < 0) {
-        // PHP 5 - create a handler to throw the exception directly.
-        assert_options(ASSERT_CALLBACK, function($file, $line, $code, $message) {
-          if (empty($message)) {
-            $message = $code;
-          }
-          throw new \AssertionError($message, 0, NULL, $file, $line);
-        });
-      }
-      else {
-        // PHP 7 - just turn exception throwing on.
-        assert_options(ASSERT_EXCEPTION, TRUE);
-      }
+  public static function register() {
+    // Since we're using exceptions, turn error warnings off.
+    assert_options(ASSERT_WARNING, FALSE);
+
+    if (version_compare(PHP_VERSION, '7.0.0-dev') < 0) {
+      // PHP 5 - create a handler to throw the exception directly.
+      assert_options(ASSERT_CALLBACK, function($file, $line, $code, $message) {
+        if (empty($message)) {
+          $message = $code;
+        }
+        throw new \AssertionError($message, 0, NULL, $file, $line);
+      });
+    }
+    else {
+      // PHP 7 - just turn exception throwing on.
+      assert_options(ASSERT_EXCEPTION, TRUE);
     }
-
   }
 
 }
+
+}
diff -u b/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
--- b/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -848,7 +848,7 @@
         // Simpletest's internal browser.
         define('DRUPAL_TEST_IN_CHILD_SITE', TRUE);
 
-        // Webtests are to be conducted with runtime assertions active.
+        // Web tests are to be conducted with runtime assertions active.
         assert_options(ASSERT_ACTIVE, TRUE);
         // Now synchronize PHP 5 and 7's handling of assertions as much as
         // possible.
diff -u b/core/modules/simpletest/src/Tests/SimpleTestTest.php b/core/modules/simpletest/src/Tests/SimpleTestTest.php
--- b/core/modules/simpletest/src/Tests/SimpleTestTest.php
+++ b/core/modules/simpletest/src/Tests/SimpleTestTest.php
@@ -169,7 +169,8 @@
     try {
       assert(FALSE, 'Lorem Ipsum');
       $this->fail('Runtime assertions are not working.');
-    } catch (\AssertionError $e) {
+    }
+    catch (\AssertionError $e) {
       $this->assertEqual($e->getMessage(), 'Lorem Ipsum', 'Runtime assertions Enabled and running.');
     }
     // This causes the second of the sixteen passes asserted in