diff --git a/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php b/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php
index 2230770..a7b6d3d 100644
--- a/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php
+++ b/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipeTestController.php
@@ -3,7 +3,7 @@
 namespace Drupal\big_pipe_test;
 
 use Drupal\big_pipe\Render\BigPipeMarkup;
-use Drupal\big_pipe\Tests\BigPipePlaceholderTestCases;
+use Drupal\Tests\big_pipe\Functional\BigPipePlaceholderTestCases;
 use Drupal\big_pipe_test\EventSubscriber\BigPipeTestSubscriber;
 
 class BigPipeTestController {
@@ -61,7 +61,7 @@ public static function nope() {
   /**
    * A page with multiple occurrences of the same placeholder.
    *
-   * @see \Drupal\big_pipe\Tests\BigPipeTest::testBigPipeMultipleOccurrencePlaceholders()
+   * @see \Drupal\Tests\big_pipe\Functional\BigPipeTest::testBigPipeMultipleOccurrencePlaceholders()
    *
    * @return array
    */
@@ -134,7 +134,7 @@ public static function responseException() {
   /**
    * #lazy_builder callback; returns the current count.
    *
-   * @see \Drupal\big_pipe\Tests\BigPipeTest::testBigPipeMultipleOccurrencePlaceholders()
+   * @see \Drupal\Tests\big_pipe\Functional\BigPipeTest::testBigPipeMultipleOccurrencePlaceholders()
    *
    * @return array
    *   The render array.
diff --git a/core/modules/big_pipe/src/Tests/BigPipePlaceholderTestCases.php b/core/modules/big_pipe/tests/src/Functional/BigPipePlaceholderTestCases.php
similarity index 98%
rename from core/modules/big_pipe/src/Tests/BigPipePlaceholderTestCases.php
rename to core/modules/big_pipe/tests/src/Functional/BigPipePlaceholderTestCases.php
index 69ec86f..ac2d6d4 100644
--- a/core/modules/big_pipe/src/Tests/BigPipePlaceholderTestCases.php
+++ b/core/modules/big_pipe/tests/src/Functional/BigPipePlaceholderTestCases.php
@@ -5,7 +5,7 @@
  * Contains \Drupal\Tests\big_pipe\Unit\Render\Placeholder\BigPipePlaceholderTestCases.
  */
 
-namespace Drupal\big_pipe\Tests;
+namespace Drupal\Tests\big_pipe\Functional;
 
 use Drupal\big_pipe\Render\BigPipeMarkup;
 use Drupal\Core\Session\AccountInterface;
@@ -19,9 +19,9 @@
  * - Unit test:
  *   \Drupal\Tests\big_pipe\Unit\Render\Placeholder\BigPipeStrategyTest
  * - Integration test for BigPipe with JS on:
- *   \Drupal\big_pipe\Tests\BigPipeTest::testBigPipe()
+ *   \Drupal\Tests\big_pipe\Functional\BigPipeTest::testBigPipe()
  * - Integration test for BigPipe with JS off:
- *   \Drupal\big_pipe\Tests\BigPipeTest::testBigPipeNoJs()
+ *   \Drupal\Tests\big_pipe\Functional\BigPipeTest::testBigPipeNoJs()
  */
 class BigPipePlaceholderTestCases {
 
@@ -33,7 +33,7 @@ class BigPipePlaceholderTestCases {
    * @param \Drupal\Core\Session\AccountInterface|null $user
    *   Optional. Necessary to get the embedded AJAX/HTML responses.
    *
-   * @return \Drupal\big_pipe\Tests\BigPipePlaceholderTestCase[]
+   * @return \Drupal\Tests\big_pipe\Functional\BigPipePlaceholderTestCase[]
    */
   public static function cases(ContainerInterface $container = NULL, AccountInterface $user = NULL) {
     // Define the two types of cacheability that we expect to see. These will be
diff --git a/core/modules/big_pipe/src/Tests/BigPipeTest.php b/core/modules/big_pipe/tests/src/Functional/BigPipeTest.php
similarity index 98%
rename from core/modules/big_pipe/src/Tests/BigPipeTest.php
rename to core/modules/big_pipe/tests/src/Functional/BigPipeTest.php
index 9d2b257..580a4d8 100644
--- a/core/modules/big_pipe/src/Tests/BigPipeTest.php
+++ b/core/modules/big_pipe/tests/src/Functional/BigPipeTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\big_pipe\Tests;
+namespace Drupal\Tests\big_pipe\Functional;
 
 use Drupal\big_pipe\Render\Placeholder\BigPipeStrategy;
 use Drupal\big_pipe\Render\BigPipe;
@@ -8,7 +8,7 @@
 use Drupal\Component\Utility\Html;
 use Drupal\Core\Logger\RfcLogLevel;
 use Drupal\Core\Url;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Tests BigPipe's no-JS detection & response delivery (with and without JS).
@@ -21,7 +21,7 @@
  *
  * @group big_pipe
  */
-class BigPipeTest extends WebTestBase {
+class BigPipeTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
@@ -138,7 +138,7 @@ public function testNoJsDetection() {
    * - \Drupal\big_pipe\Render\BigPipe
    * - \Drupal\big_pipe\Render\BigPipe::sendPlaceholders()
    *
-   * @see \Drupal\big_pipe\Tests\BigPipePlaceholderTestCases
+   * @see \Drupal\Tests\big_pipe\Functional\BigPipePlaceholderTestCases
    */
   public function testBigPipe() {
     // Simulate production.
@@ -218,7 +218,7 @@ public function testBigPipe() {
    * - \Drupal\big_pipe\Render\BigPipe
    * - \Drupal\big_pipe\Render\BigPipe::sendNoJsPlaceholders()
    *
-   * @see \Drupal\big_pipe\Tests\BigPipePlaceholderTestCases
+   * @see \Drupal\Tests\big_pipe\Functional\BigPipePlaceholderTestCases
    */
   public function testBigPipeNoJs() {
     // Simulate production.
diff --git a/core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php b/core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php
index f0f40ba..4c634c2 100644
--- a/core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php
+++ b/core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php
@@ -3,7 +3,7 @@
 namespace Drupal\Tests\big_pipe\Unit\Render\Placeholder;
 
 use Drupal\big_pipe\Render\Placeholder\BigPipeStrategy;
-use Drupal\big_pipe\Tests\BigPipePlaceholderTestCases;
+use Drupal\Tests\big_pipe\Functional\BigPipePlaceholderTestCases;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Session\SessionConfigurationInterface;
 use Drupal\Tests\UnitTestCase;
@@ -59,7 +59,7 @@ public function testProcessPlaceholders(array $placeholders, $method, $route_mat
   }
 
   /**
-   * @see \Drupal\big_pipe\Tests\BigPipePlaceholderTestCases
+   * @see \Drupal\Tests\big_pipe\Functional\BigPipePlaceholderTestCases
    */
   public function placeholdersProvider() {
     $cases = BigPipePlaceholderTestCases::cases();