--- /dev/null
+<?php
+
+namespace Drupal\Tests\system\Functional\Common;
+
+use Drupal\Core\Url;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Verifies that bubbleable metadata of early rendering is not lost.
+ *
+ * @group Common
+ */
+class EarlyRenderingControllerTest extends BrowserTestBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ protected $dumpHeaders = TRUE;
+
+ /**
+ * {@inheritdoc}
+ */
+ public static $modules = ['system', 'early_rendering_controller_test'];
+
+ /**
+ * Tests theme preprocess functions being able to attach assets.
+ */
+ public function testEarlyRendering() {
+ // Render array: non-early & early.
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.render_array'));
+ $this->assertResponse(200);
+ $this->assertRaw('Hello world!');
+ $this->assertCacheTag('foo');
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.render_array.early'));
+ $this->assertResponse(200);
+ $this->assertRaw('Hello world!');
+ $this->assertCacheTag('foo');
+
+ // AjaxResponse: non-early & early.
+ // @todo Add cache tags assertion when AjaxResponse is made cacheable in
+ // https://www.drupal.org/node/956186.
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.ajax_response'));
+ $this->assertResponse(200);
+ $this->assertRaw('Hello world!');
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.ajax_response.early'));
+ $this->assertResponse(200);
+ $this->assertRaw('Hello world!');
+
+ // Basic Response object: non-early & early.
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.response'));
+ $this->assertResponse(200);
+ $this->assertRaw('Hello world!');
+ $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'foo');
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.response.early'));
+ $this->assertResponse(200);
+ $this->assertRaw('Hello world!');
+ $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'foo');
+
+ // Response object with attachments: non-early & early.
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.response-with-attachments'));
+ $this->assertResponse(200);
+ $this->assertRaw('Hello world!');
+ $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'foo');
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.response-with-attachments.early'));
+ $this->assertResponse(500);
+ $this->assertRaw('The controller result claims to be providing relevant cache metadata, but leaked metadata was detected. Please ensure you are not rendering content too early. Returned object class: Drupal\early_rendering_controller_test\AttachmentsTestResponse.');
+
+ // Cacheable Response object: non-early & early.
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.cacheable-response'));
+ $this->assertResponse(200);
+ $this->assertRaw('Hello world!');
+ $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'foo');
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.cacheable-response.early'));
+ $this->assertResponse(500);
+ $this->assertRaw('The controller result claims to be providing relevant cache metadata, but leaked metadata was detected. Please ensure you are not rendering content too early. Returned object class: Drupal\early_rendering_controller_test\CacheableTestResponse.');
+
+ // Basic domain object: non-early & early.
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.domain-object'));
+ $this->assertResponse(200);
+ $this->assertRaw('TestDomainObject');
+ $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'foo');
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.domain-object.early'));
+ $this->assertResponse(200);
+ $this->assertRaw('TestDomainObject');
+ $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'foo');
+
+ // Basic domain object with attachments: non-early & early.
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.domain-object-with-attachments'));
+ $this->assertResponse(200);
+ $this->assertRaw('AttachmentsTestDomainObject');
+ $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'foo');
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.domain-object-with-attachments.early'));
+ $this->assertResponse(500);
+ $this->assertRaw('The controller result claims to be providing relevant cache metadata, but leaked metadata was detected. Please ensure you are not rendering content too early. Returned object class: Drupal\early_rendering_controller_test\AttachmentsTestDomainObject.');
+
+ // Cacheable Response object: non-early & early.
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.cacheable-domain-object'));
+ $this->assertResponse(200);
+ $this->assertRaw('CacheableTestDomainObject');
+ $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'foo');
+ $this->drupalGet(Url::fromRoute('early_rendering_controller_test.cacheable-domain-object.early'));
+ $this->assertResponse(500);
+ $this->assertRaw('The controller result claims to be providing relevant cache metadata, but leaked metadata was detected. Please ensure you are not rendering content too early. Returned object class: Drupal\early_rendering_controller_test\CacheableTestDomainObject.');
+
+ // The exceptions are expected. Do not interpret them as a test failure.
+ // Not using File API; a potential error must trigger a PHP warning.
+ unlink($this->root . '/' . $this->siteDirectory . '/error.log');
+ }
+
+}