diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index d8b54af..d4316b6 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -1604,8 +1604,7 @@ function install_retrieve_file($uri, $destination) {
  */
 function install_check_localization_server($uri) {
   try {
-    $request = \Drupal::httpClient()->head($uri);
-    $request->send();
+    \Drupal::httpClient()->head($uri);
     return TRUE;
   }
   catch (RequestException $e) {
diff --git a/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsAdminTest.php b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsAdminTest.php
index 89606bc..d6dfbab 100644
--- a/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsAdminTest.php
+++ b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsAdminTest.php
@@ -86,16 +86,16 @@ function testStatisticsSettings() {
     $post = array('nid' => $nid);
     global $base_url;
     $stats_path = $base_url . '/' . drupal_get_path('module', 'statistics'). '/statistics.php';
-    $this->client->post($stats_path, array(), $post)->send();
+    $this->client->post($stats_path, array(), $post);
 
     // Hit the node again (the counter is incremented after the hit, so
     // "1 view" will actually be shown when the node is hit the second time).
     $this->drupalGet('node/' . $this->test_node->id());
-    $this->client->post($stats_path, array(), $post)->send();
+    $this->client->post($stats_path, array(), $post);
     $this->assertText('1 view', 'Node is viewed once.');
 
     $this->drupalGet('node/' . $this->test_node->id());
-    $this->client->post($stats_path, array(), $post)->send();
+    $this->client->post($stats_path, array(), $post);
     $this->assertText('2 views', 'Node is viewed 2 times.');
   }
 
@@ -111,7 +111,7 @@ function testDeleteNode() {
     $post = array('nid' => $nid);
     global $base_url;
     $stats_path = $base_url . '/' . drupal_get_path('module', 'statistics'). '/statistics.php';
-    $this->client->post($stats_path, array(), $post)->send();
+    $this->client->post($stats_path, array(), $post);
 
     $result = db_select('node_counter', 'n')
       ->fields('n', array('nid'))
@@ -145,9 +145,9 @@ function testExpiredLogs() {
     $post = array('nid' => $nid);
     global $base_url;
     $stats_path = $base_url . '/' . drupal_get_path('module', 'statistics'). '/statistics.php';
-    $this->client->post($stats_path, array(), $post)->send();
+    $this->client->post($stats_path, array(), $post);
     $this->drupalGet('node/' . $this->test_node->id());
-    $this->client->post($stats_path, array(), $post)->send();
+    $this->client->post($stats_path, array(), $post);
     $this->assertText('1 view', 'Node is viewed once.');
 
     // statistics_cron() will subtract
diff --git a/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsLoggingTest.php b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsLoggingTest.php
index f30a69a..a2704d8 100644
--- a/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsLoggingTest.php
+++ b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsLoggingTest.php
@@ -93,7 +93,7 @@ function testLogging() {
     // Manually call statistics.php to simulate ajax data collection behavior.
     $nid = $this->node->id();
     $post = array('nid' => $nid);
-    $this->client->post($stats_path, array(), $post)->send();
+    $this->client->post($stats_path, array(), $post);
     $node_counter = statistics_get($this->node->id());
     $this->assertIdentical($node_counter['totalcount'], '1');
   }
diff --git a/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsReportsTest.php b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsReportsTest.php
index 9f90a27..fed4bdc 100644
--- a/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsReportsTest.php
+++ b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsReportsTest.php
@@ -38,7 +38,7 @@ function testPopularContentBlock() {
     $stats_path = $base_url . '/' . drupal_get_path('module', 'statistics'). '/statistics.php';
     $client = \Drupal::httpClient();
     $client->setDefaultOption('config/curl', array(CURLOPT_TIMEOUT => 10));
-    $client->post($stats_path, $headers, $post)->send();
+    $client->post($stats_path, $headers, $post);
 
     // Configure and save the block.
     $this->drupalPlaceBlock('statistics_popular_block', array(
diff --git a/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsTokenReplaceTest.php b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsTokenReplaceTest.php
index e6d17cb..e692173 100644
--- a/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsTokenReplaceTest.php
+++ b/core/modules/statistics/lib/Drupal/statistics/Tests/StatisticsTokenReplaceTest.php
@@ -42,7 +42,7 @@ function testStatisticsTokenReplacement() {
     $stats_path = $base_url . '/' . drupal_get_path('module', 'statistics'). '/statistics.php';
     $client = \Drupal::httpClient();
     $client->setDefaultOption('config/curl', array(CURLOPT_TIMEOUT => 10));
-    $client->post($stats_path, $headers, $post)->send();
+    $client->post($stats_path, $headers, $post);
     $statistics = statistics_get($node->id());
 
     // Generate and test tokens.
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 06082ac..f84a6c6 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -1682,7 +1682,6 @@ function system_retrieve_file($url, $destination = NULL, $managed = FALSE, $repl
   try {
     $data = \Drupal::httpClient()
       ->get($url)
-      ->send()
       ->getBody(TRUE);
     $local = $managed ? file_save_data($data, $path, $replace) : file_unmanaged_save_data($data, $path, $replace);
   }
diff --git a/core/tests/Drupal/Tests/Core/Cache/CacheContextsTest.php b/core/tests/Drupal/Tests/Core/Cache/CacheContextsTest.php
index 6e5864d..e430965 100644
--- a/core/tests/Drupal/Tests/Core/Cache/CacheContextsTest.php
+++ b/core/tests/Drupal/Tests/Core/Cache/CacheContextsTest.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Cache\CacheContexts;
 use Drupal\Core\Cache\CacheContextInterface;
+use Drupal\Tests\UnitTestCase;
 
 /**
  * Fake cache context class.
@@ -38,7 +39,7 @@ public function getContext() {
  *
  * @see \Drupal\Core\Cache\CacheContexts
  */
-class CacheContextsTest extends \PHPUnit_Framework_TestCase {
+class CacheContextsTest extends UnitTestCase {
 
   public static function getInfo() {
     return array(