diff --git a/core/modules/history/src/Tests/HistoryTest.php b/core/modules/history/src/Tests/HistoryTest.php
index 7b6254e..3f001b7 100644
--- a/core/modules/history/src/Tests/HistoryTest.php
+++ b/core/modules/history/src/Tests/HistoryTest.php
@@ -5,9 +5,7 @@
 use Drupal\Component\Serialization\Json;
 use Drupal\Core\Url;
 use Drupal\simpletest\WebTestBase;
-use Psr\Http\Message\ResponseInterface;
 use Symfony\Component\Serializer\Encoder\JsonEncoder;
-use Symfony\Component\Serializer\Encoder\XmlEncoder;
 use Symfony\Component\Serializer\Serializer;
 
 /**
@@ -61,7 +59,7 @@ protected function setUp() {
     $this->testNode = $this->drupalCreateNode(array('type' => 'page', 'uid' => $this->user->id()));
     $this->client = \Drupal::service('http_client_factory')
       ->fromOptions(['config/curl' => [CURLOPT_TIMEOUT => 10]]);
-    $encoders = [new JsonEncoder(), new XmlEncoder()];
+    $encoders = [new JsonEncoder()];
     $this->serializer = new Serializer([], $encoders);
   }
 
@@ -71,7 +69,7 @@ protected function setUp() {
    * @param array $node_ids
    *   An array of node IDs.
    *
-   * @return ResponseInterface
+   * @return \Psr\Http\Message\ResponseInterface
    *   The response object.
    */
   protected function getNodeReadTimestamps(array $node_ids) {
@@ -83,9 +81,10 @@ protected function getNodeReadTimestamps(array $node_ids) {
     $url = Url::fromRoute('history.get_last_node_view')
       ->setAbsolute();
     $this->verbose($this->serializer->encode($post, 'json'));
-    return \Drupal::httpClient()->post($url->toString(), [
+    return $this->client->post($url->toString(), [
       'body' => $this->serializer->encode($post, 'json'),
       'headers' => [
+        'Accept' => 'application/json',
         'Content-Type' => 'application/x-www-form-urlencoded',
       ]
     ]);
@@ -102,7 +101,7 @@ protected function getNodeReadTimestamps(array $node_ids) {
    */
   protected function markNodeAsRead($node_id) {
     $url = Url::fromRoute('history.read_node', array('node' => $node_id), array('absolute' => TRUE))->toString();
-    return \Drupal::httpClient()->post($url, [
+    return $this->client->post($url, [
       'headers' => array(
         'Accept' => 'application/json',
       ),
@@ -114,7 +113,7 @@ protected function markNodeAsRead($node_id) {
   /**
    * Verifies that the history endpoints work.
    */
-  function testHistory() {
+  public function testHistory() {
     $nid = $this->testNode->id();
 
     // Retrieve "last read" timestamp for test node, for the current user.