--- /dev/null
+<?php
+
+namespace Drupal\system\Tests\Form;
+
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\Core\Url;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\simpletest\WebTestBase;
+use Drupal\field\Entity\FieldStorageConfig;
+
+/**
+ * Tests functionality of \Drupal\Core\Form\FormBuilderInterface::rebuildForm().
+ *
+ * @group Form
+ * @todo Add tests for other aspects of form rebuilding.
+ */
+class RebuildTest extends WebTestBase {
+
+ /**
+ * Modules to enable.
+ *
+ * @var array
+ */
+ public static $modules = ['node', 'form_test'];
+
+ /**
+ * A user for testing.
+ *
+ * @var \Drupal\user\UserInterface
+ */
+ protected $webUser;
+
+ protected function setUp() {
+ parent::setUp();
+
+ $this->drupalCreateContentType(['type' => 'page', 'name' => 'Basic page']);
+
+ $this->webUser = $this->drupalCreateUser(['access content']);
+ $this->drupalLogin($this->webUser);
+ }
+
+ /**
+ * Tests preservation of values.
+ */
+ public function testRebuildPreservesValues() {
+ $edit = [
+ 'checkbox_1_default_off' => TRUE,
+ 'checkbox_1_default_on' => FALSE,
+ 'text_1' => 'foo',
+ ];
+ $this->drupalPostForm('form-test/form-rebuild-preserve-values', $edit, 'Add more');
+
+ // Verify that initial elements retained their submitted values.
+ $this->assertFieldChecked('edit-checkbox-1-default-off', 'A submitted checked checkbox retained its checked state during a rebuild.');
+ $this->assertNoFieldChecked('edit-checkbox-1-default-on', 'A submitted unchecked checkbox retained its unchecked state during a rebuild.');
+ $this->assertFieldById('edit-text-1', 'foo', 'A textfield retained its submitted value during a rebuild.');
+
+ // Verify that newly added elements were initialized with their default values.
+ $this->assertFieldChecked('edit-checkbox-2-default-on', 'A newly added checkbox was initialized with a default checked state.');
+ $this->assertNoFieldChecked('edit-checkbox-2-default-off', 'A newly added checkbox was initialized with a default unchecked state.');
+ $this->assertFieldById('edit-text-2', 'DEFAULT 2', 'A newly added textfield was initialized with its default value.');
+ }
+
+ /**
+ * Tests that a form's action is retained after an Ajax submission.
+ *
+ * The 'action' attribute of a form should not change after an Ajax submission
+ * followed by a non-Ajax submission, which triggers a validation error.
+ */
+ public function testPreserveFormActionAfterAJAX() {
+ // Create a multi-valued field for 'page' nodes to use for Ajax testing.
+ $field_name = 'field_ajax_test';
+ FieldStorageConfig::create([
+ 'field_name' => $field_name,
+ 'entity_type' => 'node',
+ 'type' => 'text',
+ 'cardinality' => FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED,
+ ])->save();
+ FieldConfig::create([
+ 'field_name' => $field_name,
+ 'entity_type' => 'node',
+ 'bundle' => 'page',
+ ])->save();
+ entity_get_form_display('node', 'page', 'default')
+ ->setComponent($field_name, ['type' => 'text_textfield'])
+ ->save();
+
+ // Log in a user who can create 'page' nodes.
+ $this->webUser = $this->drupalCreateUser(['create page content']);
+ $this->drupalLogin($this->webUser);
+
+ // Get the form for adding a 'page' node. Submit an "add another item" Ajax
+ // submission and verify it worked by ensuring the updated page has two text
+ // field items in the field for which we just added an item.
+ $this->drupalGet('node/add/page');
+ $this->drupalPostAjaxForm(NULL, [], ['field_ajax_test_add_more' => t('Add another item')], NULL, [], [], 'node-page-form');
+ $this->assert(count($this->xpath('//div[contains(@class, "field--name-field-ajax-test")]//input[@type="text"]')) == 2, 'AJAX submission succeeded.');
+
+ // Submit the form with the non-Ajax "Save" button, leaving the title field
+ // blank to trigger a validation error, and ensure that a validation error
+ // occurred, because this test is for testing what happens when a form is
+ // re-rendered without being re-built, which is what happens when there's
+ // a validation error.
+ $this->drupalPostForm(NULL, [], t('Save'));
+ $this->assertText('Title field is required.', 'Non-AJAX submission correctly triggered a validation error.');
+
+ // Ensure that the form contains two items in the multi-valued field, so we
+ // know we're testing a form that was correctly retrieved from cache.
+ $this->assert(count($this->xpath('//form[contains(@id, "node-page-form")]//div[contains(@class, "js-form-item-field-ajax-test")]//input[@type="text"]')) == 2, 'Form retained its state from cache.');
+
+ // Ensure that the form's action is correct.
+ $forms = $this->xpath('//form[contains(@class, "node-page-form")]');
+ $this->assertEqual(1, count($forms));
+ // Strip query params off the action before asserting.
+ $url = parse_url($forms[0]['action'])['path'];
+ $this->assertEqual(Url::fromRoute('node.add', ['node_type' => 'page'])->toString(), $url);
+ }
+
+}