Issue #2631478 by neclimdul: bootstrap.php loader can show as changed global state

core/tests/Drupal/KernelTests/KernelTestBase.php

@@ -235,8 +235,7 @@ abstract class KernelTestBase extends \PHPUnit_Framework_TestCase implements Ser
     $this->streamWrappers = array();
     \Drupal::unsetContainer();
 
-    // @see /core/tests/bootstrap.php
-    $this->classLoader = $GLOBALS['loader'];
+    $this->classLoader = require $this->root . '/autoload.php';
 
     require_once $this->root . '/core/includes/bootstrap.inc';
 

core/tests/bootstrap.php

@@ -87,8 +87,21 @@ function drupal_phpunit_get_extension_namespaces($dirs) {
 if (!defined('PHPUNIT_COMPOSER_INSTALL')) {
   define('PHPUNIT_COMPOSER_INSTALL', __DIR__ . '/../../autoload.php');
 }
-// Start with classes in known locations.
+
+/**
+ * Populate class loader with additional namespaces for tests.
+ *
+ * We run this in a function to avoid setting the class loader to a global
+ * that can change. This change can cause unpredictable false positives for
+ * phpunit's global state change watcher. The class loader can be retrieved from
+ * composer at any time by requiring autoload.php.
+ */
+function drupal_phpunit_populate_class_loader() {
+
+  /** @var \Composer\Autoload\ClassLoader $loader */
   $loader = require __DIR__ . '/../../autoload.php';
+
+  // Start with classes in known locations.
   $loader->add('Drupal\\Tests', __DIR__);
   $loader->add('Drupal\\KernelTests', __DIR__);
 
@@ -104,6 +117,12 @@ foreach ($GLOBALS['namespaces'] as $prefix => $paths) {
     $loader->addPsr4($prefix, $paths);
   }
 
+  return $loader;
+};
+
+// Do class loader population.
+drupal_phpunit_populate_class_loader();
+
 // Set sane locale settings, to ensure consistent string, dates, times and
 // numbers handling.
 // @see \Drupal\Core\DrupalKernel::bootEnvironment()