Andy Blum
--- a/core/tests/Drupal/TestSite/TestSiteOliveroInstallTestScript.php
+++ b/core/tests/Drupal/TestSite/TestSiteOliveroInstallTestScript.php
+    ]);
+    $process->setTimeout(60);
+    return $process;
+  }

  /**
   * {@inheritdoc}
   */
-  public function setup() {
+  public function setup(): void {
+
    // Install required module for the Olivero front page.
    $module_installer = \Drupal::service('module_installer');
    assert($module_installer instanceof ModuleInstallerInterface);
    $module_installer->install(['olivero_test']);
+    $module_installer->install(['nightwatch_theme_install_utility']);
-    $module_installer->install(['olivero_test']);
-    $module_installer->install(['nightwatch_theme_install_utility']);
+    $module_installer->install(['olivero_test', 'nightwatch_theme_install_utility']);
--- a/core/tests/Drupal/TestSite/TestSiteOliveroInstallTestScript.php
+++ b/core/tests/Drupal/TestSite/TestSiteOliveroInstallTestScript.php
   * {@inheritdoc}
   */
-  public function setup() {
+  public function setup(): void {
+
    // Install required module for the Olivero front page.
    $module_installer = \Drupal::service('module_installer');
    assert($module_installer instanceof ModuleInstallerInterface);
    $module_installer->install(['olivero_test']);
+    $module_installer->install(['nightwatch_theme_install_utility']);

    // Install Olivero and set it as the default theme.
    $theme_installer = \Drupal::service('theme_installer');
    assert($theme_installer instanceof ThemeInstallerInterface);
    $theme_installer->install(['olivero'], TRUE);
+    $theme_installer->install(['test_custom_theme'], TRUE);
-    $theme_installer->install(['olivero'], TRUE);
-    $theme_installer->install(['test_custom_theme'], TRUE);
+    $theme_installer->install(['olivero', 'test_custom_theme'], TRUE);
--- a/core/tests/Drupal/TestSite/TestPreinstallInterface.php
+++ b/core/tests/Drupal/TestSite/TestPreinstallInterface.php
   * @param string $site_directory
   *   The site directory.
   *
+   * @return void
+   *   No return value.
+   *
   * @see \Drupal\TestSite\TestSiteInstallTestScript
   */
-  public function preinstall($db_prefix, $site_directory);
+  public function preinstall($db_prefix, $site_directory): void;
--- a/core/tests/Drupal/TestSite/TestPreinstallInterface.php
+++ b/core/tests/Drupal/TestSite/TestPreinstallInterface.php
   * @param string $site_directory
   *   The site directory.
   *
+   * @return void
+   *   No return value.
+   *
--- a/core/tests/Drupal/TestSite/TestSetupInterface.php
+++ b/core/tests/Drupal/TestSite/TestSetupInterface.php
   *
   * @see \Drupal\TestSite\TestSiteInstallTestScript
   */
-  public function setup();
+  public function setup(): void;