diff --git a/core/modules/contextual/src/Tests/ContextualDynamicContextTest.php b/core/modules/contextual/tests/src/Functional/ContextualDynamicContextTest.php
similarity index 75%
rename from core/modules/contextual/src/Tests/ContextualDynamicContextTest.php
rename to core/modules/contextual/tests/src/Functional/ContextualDynamicContextTest.php
index 00ade5a..52ca648 100644
--- a/core/modules/contextual/src/Tests/ContextualDynamicContextTest.php
+++ b/core/modules/contextual/tests/src/Functional/ContextualDynamicContextTest.php
@@ -1,12 +1,13 @@
 <?php
 
-namespace Drupal\contextual\Tests;
+namespace Drupal\Tests\contextual\Functional;
 
 use Drupal\Component\Serialization\Json;
 use Drupal\Core\Url;
 use Drupal\language\Entity\ConfigurableLanguage;
-use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Template\Attribute;
+use Drupal\Tests\BrowserTestBase;
+use GuzzleHttp\Cookie\CookieJar;
 
 /**
  * Tests if contextual links are showing on the front page depending on
@@ -14,7 +15,7 @@
  *
  * @group contextual
  */
-class ContextualDynamicContextTest extends WebTestBase {
+class ContextualDynamicContextTest extends BrowserTestBase {
 
   /**
    * A user with permission to access contextual links and edit content.
@@ -38,6 +39,13 @@ class ContextualDynamicContextTest extends WebTestBase {
   protected $anonymousUser;
 
   /**
+   * The Guzzle HTTP client.
+   *
+   * @var \GuzzleHttp\Client;
+   */
+  protected $client;
+
+  /**
    * Modules to enable.
    *
    * @var array
@@ -56,6 +64,7 @@ protected function setUp() {
     $this->editorUser = $this->drupalCreateUser(['access content', 'access contextual links', 'edit any article content']);
     $this->authenticatedUser = $this->drupalCreateUser(['access content', 'access contextual links']);
     $this->anonymousUser = $this->drupalCreateUser(['access content']);
+    $this->client = \Drupal::httpClient();
   }
 
   /**
@@ -89,12 +98,12 @@ public function testDifferentPermissions() {
     for ($i = 0; $i < count($ids); $i++) {
       $this->assertContextualLinkPlaceHolder($ids[$i]);
     }
-    $this->renderContextualLinks([], 'node');
-    $this->assertResponse(400);
-    $this->assertRaw('No contextual ids specified.');
+    $response = $this->renderContextualLinks([], 'node');
+    $this->assertEquals(400, $response->getStatusCode());
+    $this->assertContains('No contextual ids specified.', (string) $response->getBody());
     $response = $this->renderContextualLinks($ids, 'node');
-    $this->assertResponse(200);
-    $json = Json::decode($response);
+    $this->assertEquals(200, $response->getStatusCode());
+    $json = Json::decode((string) $response->getBody());
     $this->assertIdentical($json[$ids[0]], '<ul class="contextual-links"><li class="entitynodeedit-form"><a href="' . base_path() . 'node/1/edit">Edit</a></li></ul>');
     $this->assertIdentical($json[$ids[1]], '');
     $this->assertIdentical($json[$ids[2]], '<ul class="contextual-links"><li class="entitynodeedit-form"><a href="' . base_path() . 'node/3/edit">Edit</a></li></ul>');
@@ -112,12 +121,12 @@ public function testDifferentPermissions() {
     for ($i = 0; $i < count($ids); $i++) {
       $this->assertContextualLinkPlaceHolder($ids[$i]);
     }
-    $this->renderContextualLinks([], 'node');
-    $this->assertResponse(400);
-    $this->assertRaw('No contextual ids specified.');
+    $response = $this->renderContextualLinks([], 'node');
+    $this->assertEquals(400, $response->getStatusCode());
+    $this->assertContains('No contextual ids specified.', (string) $response->getBody());
     $response = $this->renderContextualLinks($ids, 'node');
-    $this->assertResponse(200);
-    $json = Json::decode($response);
+    $this->assertEquals(200, $response->getStatusCode());
+    $json = Json::decode((string) $response->getBody());
     $this->assertIdentical($json[$ids[0]], '');
     $this->assertIdentical($json[$ids[1]], '');
     $this->assertIdentical($json[$ids[2]], '');
@@ -129,10 +138,10 @@ public function testDifferentPermissions() {
     for ($i = 0; $i < count($ids); $i++) {
       $this->assertNoContextualLinkPlaceHolder($ids[$i]);
     }
-    $this->renderContextualLinks([], 'node');
-    $this->assertResponse(403);
-    $this->renderContextualLinks($ids, 'node');
-    $this->assertResponse(403);
+    $response = $this->renderContextualLinks([], 'node');
+    $this->assertEquals(403, $response->getStatusCode());
+    $response = $this->renderContextualLinks($ids, 'node');
+    $this->assertEquals(403, $response->getStatusCode());
 
     // Get a page where contextual links are directly rendered.
     $this->drupalGet(Url::fromRoute('menu_test.contextual_test'));
@@ -174,15 +183,38 @@ protected function assertNoContextualLinkPlaceHolder($id) {
    * @param string $current_path
    *   The Drupal path for the page for which the contextual links are rendered.
    *
-   * @return string
-   *   The response body.
+   * @return \Psr\Http\Message\ResponseInterface
+   *   The response object.
    */
   protected function renderContextualLinks($ids, $current_path) {
     $post = [];
     for ($i = 0; $i < count($ids); $i++) {
-      $post['ids[' . $i . ']'] = $ids[$i];
+      $post[] = urlencode('ids[' . $i . ']') . '=' . urlencode($ids[$i]);
     }
-    return $this->drupalPostWithFormat('contextual/render', 'json', $post, ['query' => ['destination' => $current_path]]);
+    $url = Url::fromRoute('contextual.render')
+      ->setOptions(['query' => ['_format' => 'json', 'destination' => $current_path]])
+      ->setAbsolute()
+      ->toString();
+
+    return $this->client->post($url, [
+      'http_errors' => FALSE,
+      'headers' => [
+        'Content-Type' => 'application/x-www-form-urlencoded',
+      ],
+      'cookies' => $this->getCookies(),
+      'body' => implode('&', $post),
+    ]);
+  }
+
+  /**
+   * Obtain the cookie jar.
+   *
+   * @return \GuzzleHttp\Cookie\CookieJar
+   */
+  protected function getCookies() {
+    $domain = parse_url($this->getUrl(), PHP_URL_HOST);
+    $session_id = $this->getSession()->getCookie($this->getSessionName());
+    return CookieJar::fromArray([$this->getSessionName() => $session_id], $domain);
   }
 
 }