diff --git a/core/modules/simpletest/src/UserCreationTrait.php b/core/modules/simpletest/src/UserCreationTrait.php
index 13212f9..b985d87 100644
--- a/core/modules/simpletest/src/UserCreationTrait.php
+++ b/core/modules/simpletest/src/UserCreationTrait.php
@@ -60,7 +60,8 @@ protected function createUser(array $permissions = array(), $name = NULL, $admin
 
     // Create a user assigned to that role.
     $edit = array();
-    $edit['name'] = !empty($name) ? $name : $this->getRandomGenerator()->string(8, TRUE, array($this, 'randomUsernameValidate'));
+    $edit['name'] = !empty($name) ? $name : $this->getRandomGenerator()->string(6, TRUE, array($this, 'randomUsernameValidate'));
+    $edit['name'] .= "'s";
     $edit['mail'] = $edit['name'] . '@example.com';
     // It is possible that name + @example.com is not a valid email address
     // since user names can contain whitespace and @ characters and start with a
diff --git a/core/modules/system/src/Tests/System/PageNotFoundTest.php b/core/modules/system/src/Tests/System/PageNotFoundTest.php
index b7c0609..623fd31 100644
--- a/core/modules/system/src/Tests/System/PageNotFoundTest.php
+++ b/core/modules/system/src/Tests/System/PageNotFoundTest.php
@@ -48,6 +48,6 @@ function testPageNotFound() {
     $this->drupalPostForm('admin/config/system/site-information', $edit, t('Save configuration'));
 
     $this->drupalGet($this->randomMachineName(10));
-    $this->assertText($this->adminUser->getUsername(), 'Found the custom 404 page');
+    $this->assertEscaped($this->adminUser->getUsername(), 'Found the custom 404 page');
   }
 }