diff --git a/core/modules/node/src/Tests/NodeViewTest.php b/core/modules/node/src/Tests/NodeViewTest.php
index 426fec1..18f7133 100644
--- a/core/modules/node/src/Tests/NodeViewTest.php
+++ b/core/modules/node/src/Tests/NodeViewTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\node\Tests;
 
+use Drupal\Core\Url;
+
 /**
  * Tests the node/{node} page.
  *
@@ -24,13 +26,13 @@ public function testHtmlHeadLinks() {
     $this->drupalGet($node->getSystemPath());
 
     $result = $this->xpath('//link[@rel = "version-history"]');
-    $this->assertEqual($result[0]['href'], _url("node/{$node->id()}/revisions"));
+    $this->assertEqual($result[0]['href'], Url::fromUri("base://node/{$node->id()}/revisions")->toString());
 
     $result = $this->xpath('//link[@rel = "edit-form"]');
-    $this->assertEqual($result[0]['href'], _url("node/{$node->id()}/edit"));
+    $this->assertEqual($result[0]['href'], Url::fromUri("base://node/{$node->id()}/edit")->toString());
 
     $result = $this->xpath('//link[@rel = "canonical"]');
-    $this->assertEqual($result[0]['href'], _url("node/{$node->id()}"));
+    $this->assertEqual($result[0]['href'], Url::fromUri("base://node/{$node->id()}")->toString());
   }
 
 }
diff --git a/core/modules/rest/src/Tests/AuthTest.php b/core/modules/rest/src/Tests/AuthTest.php
index bf51c00..b461979 100644
--- a/core/modules/rest/src/Tests/AuthTest.php
+++ b/core/modules/rest/src/Tests/AuthTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\rest\Tests;
 
+use Drupal\Core\Url;
 use Drupal\rest\Tests\RESTTestBase;
 
 /**
@@ -87,7 +88,7 @@ protected function basicAuthGet($path, $username, $password) {
     $out = $this->curlExec(
       array(
         CURLOPT_HTTPGET => TRUE,
-        CURLOPT_URL => _url($path, array('absolute' => TRUE)),
+        CURLOPT_URL => Url::fromUri('base://' . $path, array('absolute' => TRUE))->toString(),
         CURLOPT_NOBODY => FALSE,
         CURLOPT_HTTPAUTH => CURLAUTH_BASIC,
         CURLOPT_USERPWD => $username . ':' . $password,
diff --git a/core/modules/rest/src/Tests/CsrfTest.php b/core/modules/rest/src/Tests/CsrfTest.php
index 7ff6389..f087b65 100644
--- a/core/modules/rest/src/Tests/CsrfTest.php
+++ b/core/modules/rest/src/Tests/CsrfTest.php
@@ -5,6 +5,8 @@
 
 namespace Drupal\rest\Tests;
 
+use Drupal\Core\Url;
+
 /**
  * Tests the CSRF protection.
  *
@@ -107,7 +109,7 @@ protected function getCurlOptions() {
       CURLOPT_HTTPGET => FALSE,
       CURLOPT_POST => TRUE,
       CURLOPT_POSTFIELDS => $this->serialized,
-      CURLOPT_URL => _url('entity/' . $this->testEntityType, array('absolute' => TRUE)),
+      CURLOPT_URL => Url::fromUri('base://entity/' . $this->testEntityType, array('absolute' => TRUE))->toString(),
       CURLOPT_NOBODY => FALSE,
       CURLOPT_HTTPHEADER => array(
         "Content-Type: {$this->defaultMimeType}",
diff --git a/core/modules/rest/src/Tests/NodeTest.php b/core/modules/rest/src/Tests/NodeTest.php
index 71d4c33..48e6ab2 100644
--- a/core/modules/rest/src/Tests/NodeTest.php
+++ b/core/modules/rest/src/Tests/NodeTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\rest\Tests;
 
+use Drupal\Core\Url;
 use Drupal\rest\Tests\RESTTestBase;
 
 /**
@@ -69,7 +70,7 @@ public function testNodes() {
     $data = array(
       '_links' => array(
         'type' => array(
-          'href' => _url('rest/type/node/resttest', array('absolute' => TRUE)),
+          'href' => Url::fromUri('base://rest/type/node/resttest', array('absolute' => TRUE))->toString(),
         ),
       ),
       'title' => array(
diff --git a/core/modules/rest/src/Tests/RESTTestBase.php b/core/modules/rest/src/Tests/RESTTestBase.php
index 2fa0331..9f453d9 100644
--- a/core/modules/rest/src/Tests/RESTTestBase.php
+++ b/core/modules/rest/src/Tests/RESTTestBase.php
@@ -8,6 +8,7 @@
 namespace Drupal\rest\Tests;
 
 use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\Url;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -62,7 +63,7 @@ protected function setUp() {
   /**
    * Helper function to issue a HTTP request with simpletest's cURL.
    *
-   * @param string $url
+   * @param string $path
    *   The relative URL, e.g. "entity/node/1"
    * @param string $method
    *   HTTP method, one of GET, POST, PUT or DELETE.
@@ -71,7 +72,7 @@ protected function setUp() {
    * @param string $mime_type
    *   The MIME type of the transmitted content.
    */
-  protected function httpRequest($url, $method, $body = NULL, $mime_type = NULL) {
+  protected function httpRequest($path, $method, $body = NULL, $mime_type = NULL) {
     if (!isset($mime_type)) {
       $mime_type = $this->defaultMimeType;
     }
@@ -79,14 +80,19 @@ protected function httpRequest($url, $method, $body = NULL, $mime_type = NULL) {
       // GET the CSRF token first for writing requests.
       $token = $this->drupalGet('rest/session/token');
     }
+
+    $options = array('absolute' =>TRUE);
+
     switch ($method) {
       case 'GET':
         // Set query if there are additional GET parameters.
-        $options = isset($body) ? array('absolute' => TRUE, 'query' => $body) : array('absolute' => TRUE);
+        if (isset($body)) {
+          $options['query'] = $body;
+        }
         $curl_options = array(
           CURLOPT_HTTPGET => TRUE,
           CURLOPT_CUSTOMREQUEST => 'GET',
-          CURLOPT_URL => _url($url, $options),
+          CURLOPT_URL => $this->container->get('url_generator')->generateFromPath($path, $options),
           CURLOPT_NOBODY => FALSE,
           CURLOPT_HTTPHEADER => array('Accept: ' . $mime_type),
         );
@@ -97,7 +103,7 @@ protected function httpRequest($url, $method, $body = NULL, $mime_type = NULL) {
           CURLOPT_HTTPGET => FALSE,
           CURLOPT_POST => TRUE,
           CURLOPT_POSTFIELDS => $body,
-          CURLOPT_URL => _url($url, array('absolute' => TRUE)),
+          CURLOPT_URL => $this->container->get('url_generator')->generateFromPath($path, $options),
           CURLOPT_NOBODY => FALSE,
           CURLOPT_HTTPHEADER => array(
             'Content-Type: ' . $mime_type,
@@ -111,7 +117,7 @@ protected function httpRequest($url, $method, $body = NULL, $mime_type = NULL) {
           CURLOPT_HTTPGET => FALSE,
           CURLOPT_CUSTOMREQUEST => 'PUT',
           CURLOPT_POSTFIELDS => $body,
-          CURLOPT_URL => _url($url, array('absolute' => TRUE)),
+          CURLOPT_URL => $this->container->get('url_generator')->generateFromPath($path, $options),
           CURLOPT_NOBODY => FALSE,
           CURLOPT_HTTPHEADER => array(
             'Content-Type: ' . $mime_type,
@@ -125,7 +131,7 @@ protected function httpRequest($url, $method, $body = NULL, $mime_type = NULL) {
           CURLOPT_HTTPGET => FALSE,
           CURLOPT_CUSTOMREQUEST => 'PATCH',
           CURLOPT_POSTFIELDS => $body,
-          CURLOPT_URL => _url($url, array('absolute' => TRUE)),
+          CURLOPT_URL => $this->container->get('url_generator')->generateFromPath($path, $options),
           CURLOPT_NOBODY => FALSE,
           CURLOPT_HTTPHEADER => array(
             'Content-Type: ' . $mime_type,
@@ -138,7 +144,7 @@ protected function httpRequest($url, $method, $body = NULL, $mime_type = NULL) {
         $curl_options = array(
           CURLOPT_HTTPGET => FALSE,
           CURLOPT_CUSTOMREQUEST => 'DELETE',
-          CURLOPT_URL => _url($url, array('absolute' => TRUE)),
+          CURLOPT_URL => $this->container->get('url_generator')->generateFromPath($path, $options),
           CURLOPT_NOBODY => FALSE,
           CURLOPT_HTTPHEADER => array('X-CSRF-Token: ' . $token),
         );
@@ -149,7 +155,7 @@ protected function httpRequest($url, $method, $body = NULL, $mime_type = NULL) {
     $headers = $this->drupalGetHeaders();
     $headers = implode("\n", $headers);
 
-    $this->verbose($method . ' request to: ' . $url .
+    $this->verbose($method . ' request to: ' . $path .
       '<hr />Code: ' . curl_getinfo($this->curlHandle, CURLINFO_HTTP_CODE) .
       '<hr />Response headers: ' . $headers .
       '<hr />Response body: ' . $response);
diff --git a/core/modules/serialization/src/Tests/EntityResolverTest.php b/core/modules/serialization/src/Tests/EntityResolverTest.php
index 2bf4ed9..92242fd 100644
--- a/core/modules/serialization/src/Tests/EntityResolverTest.php
+++ b/core/modules/serialization/src/Tests/EntityResolverTest.php
@@ -6,6 +6,8 @@
 
 namespace Drupal\serialization\Tests;
 
+use Drupal\Core\Url;
+
 /**
  * Tests that entities references can be resolved.
  *
@@ -58,16 +60,16 @@ function testUuidEntityResolver() {
     $entity->set('field_test_entity_reference', array(array('target_id' => 1)));
     $entity->save();
 
-    $field_uri = _url('rest/relation/entity_test_mulrev/entity_test_mulrev/field_test_entity_reference', array('absolute' => TRUE));
+    $field_uri = Url::fromUri('base://rest/relation/entity_test_mulrev/entity_test_mulrev/field_test_entity_reference', array('absolute' => TRUE))->toString();
 
     $data = array(
       '_links' => array(
         'type' => array(
-          'href' => _url('rest/type/entity_test_mulrev/entity_test_mulrev', array('absolute' => TRUE)),
+          'href' => Url::fromUri('base://rest/type/entity_test_mulrev/entity_test_mulrev', array('absolute' => TRUE))->toString(),
         ),
         $field_uri => array(
           array(
-            'href' => _url('entity/entity_test_mulrev/' . $entity->id()),
+            'href' => Url::fromUri('base://entity/entity_test_mulrev/' . $entity->id())->toString(),
           ),
         ),
       ),
@@ -75,7 +77,7 @@ function testUuidEntityResolver() {
         $field_uri => array(
           array(
             '_links' => array(
-              'self' => _url('entity/entity_test_mulrev/' . $entity->id()),
+              'self' => Url::fromUri('base://entity/entity_test_mulrev/' . $entity->id())->toString(),
             ),
             'uuid' => array(
               array(
diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index d2b31ae..59f2edf 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -26,6 +26,7 @@
 use Drupal\Core\Site\Settings;
 use Drupal\Core\StreamWrapper\PublicStream;
 use Drupal\Core\Datetime\DrupalDateTime;
+use Drupal\Core\Url;
 use Drupal\block\Entity\Block;
 use Symfony\Component\HttpFoundation\Request;
 use Drupal\user\Entity\Role;
@@ -1948,11 +1949,22 @@ protected function drupalProcessAjaxResponse($content, array $ajax_response, arr
    *
    * @see WebTestBase::getAjaxPageStatePostData()
    * @see WebTestBase::curlExec()
-   * @see _url()
+   * @see \Drupal\Core\Url::fromUri()
    */
   protected function drupalPost($path, $accept, array $post, $options = array()) {
+    $options['absolute'] = TRUE;
+
+    // The URL generator service is not necessarily available yet; e.g., in
+    // interactive installer tests.
+    if ($this->container->has('url_generator')) {
+      $url = $this->container->get('url_generator')->generateFromPath($path, $options);
+    }
+    else {
+      $url = $this->getAbsoluteUrl($path);
+    }
+
     return $this->curlExec(array(
-      CURLOPT_URL => _url($path, $options + array('absolute' => TRUE)),
+      CURLOPT_URL => $url,
       CURLOPT_POST => TRUE,
       CURLOPT_POSTFIELDS => $this->serializePostValues($post),
       CURLOPT_HTTPHEADER => array(
diff --git a/core/modules/system/src/Tests/Cache/PageCacheTagsTestBase.php b/core/modules/system/src/Tests/Cache/PageCacheTagsTestBase.php
index 1da3a56..48f7e52 100644
--- a/core/modules/system/src/Tests/Cache/PageCacheTagsTestBase.php
+++ b/core/modules/system/src/Tests/Cache/PageCacheTagsTestBase.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\system\Tests\Cache;
 
+use Drupal\Core\Url;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Component\Utility\String;
 
@@ -53,7 +54,7 @@ protected function verifyPageCache($path, $hit_or_miss, $tags = FALSE) {
     $this->assertEqual($this->drupalGetHeader('X-Drupal-Cache'), $hit_or_miss, $message);
 
     if ($hit_or_miss === 'HIT' && is_array($tags)) {
-      $cid_parts = array(_url($path, array('absolute' => TRUE)), 'html');
+      $cid_parts = array(Url::fromUri('base://' . $path, array('absolute' => TRUE))->toString(), 'html');
       $cid = implode(':', $cid_parts);
       $cache_entry = \Drupal::cache('render')->get($cid);
       sort($cache_entry->tags);
diff --git a/core/modules/system/src/Tests/Common/UrlTest.php b/core/modules/system/src/Tests/Common/UrlTest.php
index efc01c6..ad9ce96 100644
--- a/core/modules/system/src/Tests/Common/UrlTest.php
+++ b/core/modules/system/src/Tests/Common/UrlTest.php
@@ -36,12 +36,12 @@ function testLinkXSS() {
     $text = $this->randomMachineName();
     $path = "<SCRIPT>alert('XSS')</SCRIPT>";
     $link = _l($text, $path);
-    $sanitized_path = check_url(_url($path));
+    $sanitized_path = check_url(Url::fromUri('base://' . $path)->toString());
     $this->assertTrue(strpos($link, $sanitized_path) !== FALSE, format_string('XSS attack @path was filtered by _l().', array('@path' => $path)));
 
     // Test _url().
-    $link = _url($path);
-    $sanitized_path = check_url(_url($path));
+    $link = Url::fromUri('base://' . $path)->toString();
+    $sanitized_path = check_url(Url::fromUri('base://' . $path)->toString());
     $this->assertTrue(strpos($link, $sanitized_path) !== FALSE, format_string('XSS attack @path was filtered by #theme', ['@path' => $path]));
   }
 
@@ -257,30 +257,30 @@ function testExternalUrls() {
 
     // Verify external URL can contain a fragment.
     $url = $test_url . '#drupal';
-    $result = _url($url);
+    $result = Url::fromUri($url)->toString();
     $this->assertEqual($url, $result, 'External URL with fragment works without a fragment in $options.');
 
     // Verify fragment can be overidden in an external URL.
     $url = $test_url . '#drupal';
     $fragment = $this->randomMachineName(10);
-    $result = _url($url, array('fragment' => $fragment));
+    $result = Url::fromUri($url, array('fragment' => $fragment))->toString();
     $this->assertEqual($test_url . '#' . $fragment, $result, 'External URL fragment is overidden with a custom fragment in $options.');
 
     // Verify external URL can contain a query string.
     $url = $test_url . '?drupal=awesome';
-    $result = _url($url);
+    $result = Url::fromUri($url)->toString();
     $this->assertEqual($url, $result, 'External URL with query string works without a query string in $options.');
 
     // Verify external URL can be extended with a query string.
     $url = $test_url;
     $query = array($this->randomMachineName(5) => $this->randomMachineName(5));
-    $result = _url($url, array('query' => $query));
+    $result = Url::fromUri($url, array('query' => $query))->toString();
     $this->assertEqual($url . '?' . http_build_query($query, '', '&'), $result, 'External URL can be extended with a query string in $options.');
 
     // Verify query string can be extended in an external URL.
     $url = $test_url . '?drupal=awesome';
     $query = array($this->randomMachineName(5) => $this->randomMachineName(5));
-    $result = _url($url, array('query' => $query));
+    $result = Url::fromUri($url, array('query' => $query))->toString();
     $this->assertEqual($url . '&' . http_build_query($query, '', '&'), $result, 'External URL query string can be extended with a custom query string in $options.');
   }
 }
diff --git a/core/modules/system/src/Tests/Menu/LocalTasksTest.php b/core/modules/system/src/Tests/Menu/LocalTasksTest.php
index fc61315..37b44d8 100644
--- a/core/modules/system/src/Tests/Menu/LocalTasksTest.php
+++ b/core/modules/system/src/Tests/Menu/LocalTasksTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\system\Tests\Menu;
 
+use Drupal\Core\Url;
 use Drupal\simpletest\WebTestBase;
 
 /**
@@ -34,7 +35,7 @@ protected function assertLocalTasks(array $hrefs, $level = 0) {
     ));
     $this->assertTrue(count($elements), 'Local tasks found.');
     foreach ($hrefs as $index => $element) {
-      $expected = _url($hrefs[$index]);
+      $expected = Url::fromUri('base://' . $hrefs[$index])->toString();
       $method = ($elements[$index]['href'] == $expected ? 'pass' : 'fail');
       $this->{$method}(format_string('Task @number href @value equals @expected.', array(
         '@number' => $index + 1,
diff --git a/core/modules/system/src/Tests/Menu/MenuTestBase.php b/core/modules/system/src/Tests/Menu/MenuTestBase.php
index 2478af3..4cb9fda 100644
--- a/core/modules/system/src/Tests/Menu/MenuTestBase.php
+++ b/core/modules/system/src/Tests/Menu/MenuTestBase.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Tests\Menu;
 
 use Drupal\Component\Utility\String;
+use Drupal\Core\Url;
 use Drupal\simpletest\WebTestBase;
 
 abstract class MenuTestBase extends WebTestBase {
@@ -64,7 +65,12 @@ protected function assertBreadcrumbParts($trail) {
     // this test would go into an infinite loop, so we need to check that too.
     while ($trail && !empty($parts)) {
       foreach ($trail as $path => $title) {
-        $url = _url($path);
+        if ($path == '') {
+          $url = Url::fromRoute('<front>')->toString();
+        }
+        else {
+          $url = Url::fromUri('base://' . $path)->toString();
+        }
         $part = array_shift($parts);
         $pass = ($pass && $part['href'] === $url && $part['text'] === String::checkPlain($title));
       }
@@ -101,7 +107,7 @@ protected function assertMenuActiveTrail($tree, $last_active) {
         $part_xpath .= 'li[contains(@class, :class)]/a[contains(@href, :href) and contains(text(), :title)]';
         $part_args = array(
           ':class' => 'active-trail',
-          ':href' => _url($link_path),
+          ':href' => Url::fromUri('base://' . $link_path)->toString(),
           ':title' => $link_title,
         );
         $xpath .= $this->buildXPathQuery($part_xpath, $part_args);
@@ -121,7 +127,7 @@ protected function assertMenuActiveTrail($tree, $last_active) {
     $args = array(
       ':class-trail' => 'active-trail',
       ':class-active' => 'active',
-      ':href' => _url($active_link_path),
+      ':href' => Url::fromUri('base://' . $active_link_path)->toString(),
       ':title' => $active_link_title,
     );
     $elements = $this->xpath($xpath, $args);
diff --git a/core/modules/update/src/Tests/UpdateCoreTest.php b/core/modules/update/src/Tests/UpdateCoreTest.php
index 6d32245..637949d 100644
--- a/core/modules/update/src/Tests/UpdateCoreTest.php
+++ b/core/modules/update/src/Tests/UpdateCoreTest.php
@@ -190,7 +190,7 @@ function testDatestampMismatch() {
   function testModulePageRunCron() {
     $this->setSystemInfo('8.0.0');
     \Drupal::config('update.settings')
-      ->set('fetch.url', _url('update-test', array('absolute' => TRUE)))
+      ->set('fetch.url', Url::fromUri('base://update-test', array('absolute' => TRUE))->toString())
       ->save();
     \Drupal::config('update_test.settings')
       ->set('xml_map', array('drupal' => '0.0'))
@@ -208,7 +208,7 @@ function testModulePageUpToDate() {
     $this->setSystemInfo('8.0.0');
     // Instead of using refreshUpdateStatus(), set these manually.
     \Drupal::config('update.settings')
-      ->set('fetch.url', _url('update-test', array('absolute' => TRUE)))
+      ->set('fetch.url', Url::fromUri('base://update-test', array('absolute' => TRUE))->toString())
       ->save();
     \Drupal::config('update_test.settings')
       ->set('xml_map', array('drupal' => '0.0'))
@@ -229,7 +229,7 @@ function testModulePageRegularUpdate() {
     $this->setSystemInfo('8.0.0');
     // Instead of using refreshUpdateStatus(), set these manually.
     \Drupal::config('update.settings')
-      ->set('fetch.url', _url('update-test', array('absolute' => TRUE)))
+      ->set('fetch.url', Url::fromUri('base://update-test', array('absolute' => TRUE))->toString())
       ->save();
     \Drupal::config('update_test.settings')
       ->set('xml_map', array('drupal' => '0.1'))
@@ -250,7 +250,7 @@ function testModulePageSecurityUpdate() {
     $this->setSystemInfo('8.0.0');
     // Instead of using refreshUpdateStatus(), set these manually.
     \Drupal::config('update.settings')
-      ->set('fetch.url', _url('update-test', array('absolute' => TRUE)))
+      ->set('fetch.url', Url::fromUri('base://update-test', array('absolute' => TRUE))->toString())
       ->save();
     \Drupal::config('update_test.settings')
       ->set('xml_map', array('drupal' => '0.2-sec'))
@@ -325,7 +325,7 @@ function testLanguageModuleUpdate() {
     $this->setSystemInfo('8.0.0');
     // Instead of using refreshUpdateStatus(), set these manually.
     \Drupal::config('update.settings')
-      ->set('fetch.url', _url('update-test', array('absolute' => TRUE)))
+      ->set('fetch.url', Url::fromUri('base://update-test', array('absolute' => TRUE))->toString())
       ->save();
     \Drupal::config('update_test.settings')
       ->set('xml_map', array('drupal' => '0.1'))
diff --git a/core/modules/update/src/Tests/UpdateTestBase.php b/core/modules/update/src/Tests/UpdateTestBase.php
index 0025e21..b4439d2 100644
--- a/core/modules/update/src/Tests/UpdateTestBase.php
+++ b/core/modules/update/src/Tests/UpdateTestBase.php
@@ -44,7 +44,7 @@
   protected function refreshUpdateStatus($xml_map, $url = 'update-test') {
     // Tell the Update Manager module to fetch from the URL provided by
     // update_test module.
-    \Drupal::config('update.settings')->set('fetch.url', _url($url, array('absolute' => TRUE)))->save();
+    \Drupal::config('update.settings')->set('fetch.url', Url::fromUri('base://' . $url, array('absolute' => TRUE))->toString())->save();
     // Save the map for update_test_mock_page() to use.
     \Drupal::config('update_test.settings')->set('xml_map', $xml_map)->save();
     // Manually check the update status.
diff --git a/core/modules/update/src/Tests/UpdateUploadTest.php b/core/modules/update/src/Tests/UpdateUploadTest.php
index 78a9cbd..0f57c02 100644
--- a/core/modules/update/src/Tests/UpdateUploadTest.php
+++ b/core/modules/update/src/Tests/UpdateUploadTest.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\update\Tests;
 
+use Drupal\Core\Url;
+
 /**
  * Tests the Update Manager module's upload and extraction functionality.
  *
@@ -80,7 +82,7 @@ function testUpdateManagerCoreSecurityUpdateMessages() {
       ->set('xml_map', array('drupal' => '0.2-sec'))
       ->save();
     \Drupal::config('update.settings')
-      ->set('fetch.url', _url('update-test', array('absolute' => TRUE)))
+      ->set('fetch.url', Url::fromUri('base://update-test', array('absolute' => TRUE))->toString())
       ->save();
     // Initialize the update status.
     $this->drupalGet('admin/reports/updates');