Update to Drupal 8.2.0. For more information, see https://www.drupal.org/project/drupal/releases/8.2.0

core/tests/Drupal/Tests/Component/ClassFinder/ClassFinderTest.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace Drupal\Tests\Component\ClassFinder;
+
+use Composer\Autoload\ClassLoader;
+use Drupal\Component\ClassFinder\ClassFinder;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Component\ClassFinder\ClassFinder
+ * @group ClassFinder
+ */
+class ClassFinderTest extends UnitTestCase {
+
+  /**
+   * @covers ::findFile
+   */
+  public function testFindFile() {
+    $finder = new ClassFinder();
+
+    // The full path is returned therefore only tests with
+    // assertStringEndsWith() so the test is portable.
+    $this->assertStringEndsWith('core/tests/Drupal/Tests/UnitTestCase.php', $finder->findFile(UnitTestCase::class));
+    $class = 'Not\\A\\Class';
+    $this->assertNull($finder->findFile($class));
+
+    // Register an autoloader that can find this class.
+    $loader = new ClassLoader();
+    $loader->addClassMap([$class => __FILE__]);
+    $loader->register();
+    $this->assertEquals(__FILE__, $finder->findFile($class));
+    // This shouldn't prevent us from finding the original file.
+    $this->assertStringEndsWith('core/tests/Drupal/Tests/UnitTestCase.php', $finder->findFile(UnitTestCase::class));
+
+    // Clean up the additional autoloader after the test.
+    $loader->unregister();
+  }
+
+}