core/modules/simpletest/src/BrowserTestBase.php | 29 ++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/core/modules/simpletest/src/BrowserTestBase.php b/core/modules/simpletest/src/BrowserTestBase.php
index 4224421..10f1f4e 100644
--- a/core/modules/simpletest/src/BrowserTestBase.php
+++ b/core/modules/simpletest/src/BrowserTestBase.php
@@ -147,6 +147,15 @@
   protected $configImporter;
 
   /**
+   * Set to TRUE to strict check all configuration saved.
+   *
+   * @see \Drupal\Core\Config\Testing\ConfigSchemaChecker
+   *
+   * @var bool
+   */
+  protected $strictConfigSchema = TRUE;
+
+  /**
    * The random data generator.
    *
    * @var \Drupal\Component\Utility\Random
@@ -861,9 +870,23 @@ public function installDrupal() {
       file_put_contents($directory . '/settings.php', "\n\$test_class = '" . get_class($this) . "';\n" . 'include DRUPAL_ROOT . \'/\' . $site_path . \'/settings.testing.php\';' . "\n", FILE_APPEND);
     }
     $settings_services_file = DRUPAL_ROOT . '/' . $this->originalSiteDirectory . '/testing.services.yml';
-    if (file_exists($settings_services_file)) {
-      // Copy the testing-specific service overrides in place.
-      copy($settings_services_file, $directory . '/services.yml');
+    if (!file_exists($settings_services_file)) {
+      // Otherwise, use the default services as a starting point for overrides.
+      $settings_services_file = DRUPAL_ROOT . '/sites/default/default.services.yml';
+    }
+    // Copy the testing-specific service overrides in place.
+    copy($settings_services_file, $directory . '/services.yml');
+    if ($this->strictConfigSchema) {
+      // Add a listener to validate configuration schema on save.
+      $yaml = new \Symfony\Component\Yaml\Yaml();
+      $content = file_get_contents($directory . '/services.yml');
+      $services = $yaml->parse($content);
+      $services['services']['simpletest.config_schema_checker'] = [
+        'class' => 'Drupal\Core\Config\Testing\ConfigSchemaChecker',
+        'arguments' => ['@config.typed'],
+        'tags' => [['name' => 'event_subscriber']]
+      ];
+      file_put_contents($directory . '/services.yml', $yaml->dump($services));
     }
 
     // Since Drupal is bootstrapped already, install_begin_request() will not