diff --git a/core/lib/Drupal/Core/Test/TestSetupTrait.php b/core/lib/Drupal/Core/Test/TestSetupTrait.php
index 8bef66c3dc..44409078db 100644
--- a/core/lib/Drupal/Core/Test/TestSetupTrait.php
+++ b/core/lib/Drupal/Core/Test/TestSetupTrait.php
@@ -159,8 +159,6 @@ protected function changeDatabasePrefix() {
     $db_url = getenv('SIMPLETEST_DB');
     if (!empty($db_url)) {
       $database = Database::convertDbUrlToConnectionInfo($db_url, isset($this->root) ? $this->root : DRUPAL_ROOT);
-      // Ensure that the connection is added.
-      Database::removeConnection('default');
       Database::addConnectionInfo('default', 'default', $database);
     }
 
diff --git a/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php b/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php
index 8e01727fcf..933c88ef3a 100644
--- a/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php
+++ b/core/tests/Drupal/Setup/Commands/TestInstallationSetupCommand.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\Setup\Commands;
 
+use Drupal\Core\Database\Database;
 use Drupal\Core\Test\FunctionalTestSetupTrait;
 use Drupal\Core\Test\TestSetupTrait;
 use Drupal\Setup\TestSetupInterface;
@@ -24,7 +25,9 @@ class TestInstallationSetupCommand extends Command {
   }
   use RandomGeneratorTrait;
   use SessionTestTrait;
-  use TestSetupTrait;
+  use TestSetupTrait {
+    changeDatabasePrefix as protected changeDatabasePrefixTrait;
+  }
 
   /**
    * The install profile to use.
@@ -173,4 +176,13 @@ protected function installParameters() {
     return $parameters;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  protected function changeDatabasePrefix() {
+    // Ensure that we use the database from SIMPLETEST_DB environment variable.
+    Database::removeConnection('default');
+    $this->changeDatabasePrefixTrait();
+  }
+
 }
diff --git a/core/tests/bootstrap.php b/core/tests/bootstrap.php
index 97ef81ea8a..adcf5b169a 100644
--- a/core/tests/bootstrap.php
+++ b/core/tests/bootstrap.php
@@ -196,5 +196,5 @@ class_alias('\PHPUnit\Framework\MockObject\Matcher\InvokedRecorder', '\PHPUnit_F
   class_alias('\PHPUnit\Framework\SkippedTestError', '\PHPUnit_Framework_SkippedTestError');
   class_alias('\PHPUnit\Framework\TestCase', '\PHPUnit_Framework_TestCase');
   class_alias('\PHPUnit\Util\Test', '\PHPUnit_Util_Test');
-  class_alias('\PHPUnit\Util\XML', '\PHPUnit_Util_XML');
+  class_alias('\PHPUnit\Util\Xml', '\PHPUnit_Util_XML');
 }