diff --git a/core/modules/system/src/Tests/Installer/SiteSettingsFormTest.php b/core/modules/system/src/Tests/Installer/SiteSettingsFormTest.php
new file mode 100644
index 0000000..a539a22
--- /dev/null
+++ b/core/modules/system/src/Tests/Installer/SiteSettingsFormTest.php
@@ -0,0 +1,41 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Installer\SiteSettingsFormTest.
+ */
+
+namespace Drupal\system\Tests\Installer;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests the extension of the site settings form.
+ */
+class SiteSettingsFormTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('install_form_test');
+
+  public static function getInfo() {
+    return array(
+      'name' => 'SiteSettingsForm extension test',
+      'description' => 'Tests that the SiteSettingsForm can be extended.',
+      'group' => 'Installer',
+    );
+  }
+
+
+  /**
+   * Confirms that the form is extensible.
+   */
+  public function testSiteSettingsForm() {
+    $this->drupalGet('testform');
+    $this->assertResponse(200);
+  }
+
+}
diff --git a/core/modules/system/tests/modules/install_form_test/install_form_test.info.yml b/core/modules/system/tests/modules/install_form_test/install_form_test.info.yml
new file mode 100644
index 0000000..82441d1
--- /dev/null
+++ b/core/modules/system/tests/modules/install_form_test/install_form_test.info.yml
@@ -0,0 +1,6 @@
+name: 'Install Form Test'
+type: module
+description: 'Test the SiteSettingsForm for extensability.'
+package: Testing
+version: VERSION
+core: 8.x
diff --git a/core/modules/system/tests/modules/install_form_test/install_form_test.routing.yml b/core/modules/system/tests/modules/install_form_test/install_form_test.routing.yml
new file mode 100644
index 0000000..7efe325
--- /dev/null
+++ b/core/modules/system/tests/modules/install_form_test/install_form_test.routing.yml
@@ -0,0 +1,7 @@
+install_form_test.testform:
+  path: '/testform'
+  defaults:
+    _form: '\Drupal\install_form_test\Form\ExtendedForm'
+    _title: 'Extended Site Settings Form'
+  requirements:
+    _access: 'TRUE'
diff --git a/core/modules/system/tests/modules/install_form_test/src/Form/ExtendedForm.php b/core/modules/system/tests/modules/install_form_test/src/Form/ExtendedForm.php
new file mode 100644
index 0000000..7119976
--- /dev/null
+++ b/core/modules/system/tests/modules/install_form_test/src/Form/ExtendedForm.php
@@ -0,0 +1,13 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\install_form_test\Form\ExtendedForm.
+ */
+
+namespace Drupal\install_form_test\Form;
+
+use Drupal\Core\Installer\Form\SiteSettingsForm;
+
+class ExtendedForm extends SiteSettingsForm {
+}