diff -u b/core/modules/big_pipe/src/Tests/BigPipePlaceholderTestCases.php b/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipePlaceholderTestCases.php
--- b/core/modules/big_pipe/src/Tests/BigPipePlaceholderTestCases.php
+++ b/core/modules/big_pipe/tests/modules/big_pipe_test/src/BigPipePlaceholderTestCases.php
@@ -2,10 +2,10 @@
 
 /**
  * @file
- * Contains \Drupal\Tests\big_pipe\Unit\Render\Placeholder\BigPipePlaceholderTestCases.
+ * Contains \Drupal\big_pipe_test\BigPipePlaceholderTestCases.
  */
 
-namespace Drupal\big_pipe\Tests;
+namespace Drupal\big_pipe_test;
 
 use Drupal\big_pipe\Render\BigPipeMarkup;
 use Drupal\Core\Session\AccountInterface;
@@ -32,7 +32,7 @@
    * @param \Drupal\Core\Session\AccountInterface|null $user
    *   Optional. Necessary to get the embedded AJAX/HTML responses.
    *
-   * @return \Drupal\big_pipe\Tests\BigPipePlaceholderTestCase[]
+   * @return \Drupal\big_pipe_test\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 -u b/core/modules/big_pipe/tests/src/Functional/BigPipeTest.php b/core/modules/big_pipe/tests/src/Functional/BigPipeTest.php
--- b/core/modules/big_pipe/tests/src/Functional/BigPipeTest.php
+++ b/core/modules/big_pipe/tests/src/Functional/BigPipeTest.php
@@ -5,7 +5,7 @@
 use Behat\Mink\Element\NodeElement;
 use Drupal\big_pipe\Render\Placeholder\BigPipeStrategy;
 use Drupal\big_pipe\Render\BigPipe;
-use Drupal\big_pipe\Tests\BigPipePlaceholderTestCases;
+use Drupal\big_pipe_test\BigPipePlaceholderTestCases;
 use Drupal\Component\Serialization\Json;
 use Drupal\Component\Utility\Html;
 use Drupal\Core\Logger\RfcLogLevel;
@@ -138,7 +138,7 @@
    * - \Drupal\big_pipe\Render\BigPipe
    * - \Drupal\big_pipe\Render\BigPipe::sendPlaceholders()
    *
-   * @see \Drupal\Tests\big_pipe\Functional\BigPipePlaceholderTestCases
+   * @see \Drupal\big_pipe_test\BigPipePlaceholderTestCases
    */
   public function testBigPipe() {
     // Simulate production.
@@ -218,7 +218,7 @@
    * - \Drupal\big_pipe\Render\BigPipe
    * - \Drupal\big_pipe\Render\BigPipe::sendNoJsPlaceholders()
    *
-   * @see \Drupal\Tests\big_pipe\Functional\BigPipePlaceholderTestCases
+   * @see \Drupal\big_pipe_test\BigPipePlaceholderTestCases
    */
   public function testBigPipeNoJs() {
     // Simulate production.
@@ -415,7 +415,7 @@
   }
 
   /**
-   * @return \Drupal\big_pipe\Tests\BigPipePlaceholderTestCase[]
+   * @return \Drupal\big_pipe_test\BigPipePlaceholderTestCase[]
    */
   protected function getTestCases($has_session = TRUE) {
     return BigPipePlaceholderTestCases::cases($this->container, $this->rootUser);
diff -u b/core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php b/core/modules/big_pipe/tests/src/Unit/Render/Placeholder/BigPipeStrategyTest.php
--- b/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\big_pipe_test\BigPipePlaceholderTestCases;
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Session\SessionConfigurationInterface;
 use Drupal\Tests\UnitTestCase;
@@ -59,7 +59,7 @@
   }
 
   /**
-   * @see \Drupal\Tests\big_pipe\Functional\BigPipePlaceholderTestCases
+   * @see \Drupal\big_pipe_test\BigPipePlaceholderTestCases
    */
   public function placeholdersProvider() {
     $cases = BigPipePlaceholderTestCases::cases();
only in patch2:
unchanged:
--- 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 +3,6 @@
 namespace Drupal\big_pipe_test;
 
 use Drupal\big_pipe\Render\BigPipeMarkup;
-use Drupal\big_pipe\Tests\BigPipePlaceholderTestCases;
 use Drupal\big_pipe_test\EventSubscriber\BigPipeTestSubscriber;
 
 class BigPipeTestController {