Issue #1948734 by msonnabaum: Fixed Include Drupal class in PHPUnit bootstrap.

core/tests/bootstrap.php

@@ -9,5 +9,7 @@
 foreach (scandir(__DIR__ . "/../modules") as $module) {
   $loader->add('Drupal\\' . $module, __DIR__ . "/../modules/" . $module . "/lib");
 }
+
+require __DIR__ . "/../../core/lib/Drupal.php";
 // Look into removing this later.
 define('REQUEST_TIME', (int) $_SERVER['REQUEST_TIME']);