first commit

core/tests/Drupal/Tests/WaitTerminateTestTrait.php

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+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests;
+
+/**
+ * Provides a method to enforce that requests will wait for the terminate event.
+ */
+trait WaitTerminateTestTrait {
+
+  /**
+   * Specify that subsequent requests must wait for the terminate event.
+   *
+   * The terminate event is fired after a response is sent to the user agent.
+   * Tests with assertions which operate on data computed during the terminate
+   * event need to enable this.
+   */
+  protected function setWaitForTerminate() {
+    $this->container->get('state')->set('drupal.test_wait_terminate', TRUE);
+  }
+
+}