src/Tests/BigPipeNoJsDetectionTest.php | 42 +++++++++++++++++++++++++++++++---
 1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/src/Tests/BigPipeNoJsDetectionTest.php b/src/Tests/BigPipeNoJsDetectionTest.php
index f037a37..8eec073 100644
--- a/src/Tests/BigPipeNoJsDetectionTest.php
+++ b/src/Tests/BigPipeNoJsDetectionTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\big_pipe\Tests;
 
+use Drupal\Component\Serialization\Json;
 use Drupal\Component\Utility\Html;
 use Drupal\Core\Url;
 use Drupal\simpletest\WebTestBase;
@@ -115,12 +116,47 @@ class BigPipeNoJsDetectionTest extends WebTestBase {
 
     // Keys: BigPipe no-JS placeholder markup. Values: expected replacement markup.
     $expected_big_pipe_nojs_placeholders = [
-      'big_pipe_nojs_placeholder_attribute_safe:form_action_cc611e1d' => '<form class="big-pipe-test-form" data-drupal-selector="big-pipe-test-form" action="/big_pipe_test"',
+      'big_pipe_nojs_placeholder_attribute_safe:form_action_cc611e1d' => '<form class="big-pipe-test-form" data-drupal-selector="big-pipe-test-form" action="' . base_path() . 'big_pipe_test"',
     ];
     // Keys: BigPipe placeholder IDs. Values: expected AJAX response.
     $expected_big_pipe_placeholders = [
-      'callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&amp;args[0]&amp;token=a8c34b5e' => '[{"command":"settings","settings":{"ajaxPageState":{"theme":"classy","libraries":"big_pipe\/big_pipe,classy\/base,classy\/messages,core\/drupal.active-link,core\/html5shiv,core\/normalize,system\/base"},"pluralDelimiter":"\u0003","user":{"uid":"1","permissionsHash":"' . $this->container->get('user_permissions_hash_generator')->generate($this->rootUser) . '"}},"merge":true},{"command":"add_css","data":"\u003Clink rel=\u0022stylesheet\u0022 href=\u0022\/core\/themes\/classy\/css\/components\/messages.css?' . $this->container->get('state')->get('system.css_js_query_string') . '\u0022 media=\u0022all\u0022 \/\u003E\n"},{"command":"insert","method":"replaceWith","selector":"[data-big-pipe-placeholder-id=\u0022callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages\u0026args[0]\u0026token=a8c34b5e\u0022]","data":"\n    \u003Cdiv role=\u0022contentinfo\u0022 aria-label=\u0022Status message\u0022 class=\u0022messages messages--status\u0022\u003E\n                  \u003Ch2 class=\u0022visually-hidden\u0022\u003EStatus message\u003C\/h2\u003E\n                    Hello from BigPipe!\n            \u003C\/div\u003E\n    \n","settings":null}]',
-      'timecurrent-timetime' => '[{"command":"insert","method":"replaceWith","selector":"[data-big-pipe-placeholder-id=\u0022timecurrent-timetime\u0022]","data":"\u003Ctime datetime=1991-03-14\u0022\u003E\u003C\/time\u003E","settings":null}]',
+      'callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&amp;args[0]&amp;token=a8c34b5e' => Json::encode([
+        [
+          'command' => 'settings',
+          'settings' => [
+            'ajaxPageState' => [
+              'theme' => 'classy',
+              'libraries' => 'big_pipe/big_pipe,classy/base,classy/messages,core/drupal.active-link,core/html5shiv,core/normalize,system/base',
+            ],
+            'pluralDelimiter' => \Drupal\Core\StringTranslation\PluralTranslatableMarkup::DELIMITER,
+            'user' => [
+              'uid' => '1',
+              'permissionsHash' => $this->container->get('user_permissions_hash_generator')->generate($this->rootUser),
+            ],
+          ],
+          'merge' => TRUE,
+        ],
+        [
+          'command' => 'add_css',
+          'data' => '<link rel="stylesheet" href="' . base_path() . 'core/themes/classy/css/components/messages.css?' . $this->container->get('state')->get('system.css_js_query_string') . '" media="all" />' . "\n"
+        ],
+        [
+          'command' => 'insert',
+          'method' => 'replaceWith',
+          'selector' => '[data-big-pipe-placeholder-id="callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&args[0]&token=a8c34b5e"]',
+          'data' => "\n" . '    <div role="contentinfo" aria-label="Status message" class="messages messages--status">' . "\n" . '                  <h2 class="visually-hidden">Status message</h2>' . "\n" . '                    Hello from BigPipe!' . "\n" . '            </div>' . "\n    \n",
+          'settings' => NULL,
+        ],
+      ]),
+      'timecurrent-timetime' => Json::encode([
+        [
+          'command' => 'insert',
+          'method' => 'replaceWith',
+          'selector' => '[data-big-pipe-placeholder-id="timecurrent-timetime"]',
+          'data' => '<time datetime=1991-03-14"></time>',
+          'settings' => NULL,
+        ],
+      ]),
     ];
 
     // Verify the expected BigPipe no-JS placeholders have already been replaced