Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/help/tests/modules/help_test/help_test.info.yml

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+name: help_test
+type: module
+core: 8.x
+package: Testing
+dependencies:
+  - help

core/modules/help/tests/modules/help_test/help_test.module

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+<?php
+
+/**
+ * @file
+ * Test Help module.
+ */
+
+use \Drupal\Core\Routing\RouteMatchInterface;
+
+/**
+ * Implements hook_help().
+ */
+function help_test_help($route_name, RouteMatchInterface $route_match) {
+  // Do not implement a module overview page to test an empty implementation.
+  // @see \Drupal\help\Tests\HelpTest
+}

core/modules/help/tests/modules/help_test/src/SupernovaGenerator.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\help_test\SupernovaGenerator.
+ */
+
+namespace Drupal\help_test;
+
+use Drupal\Core\Routing\UrlGeneratorInterface;
+use Symfony\Component\Routing\RequestContext;
+
+/**
+ * Implements a URL generator which always thrown an exception.
+ */
+class SupernovaGenerator implements UrlGeneratorInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setContext(RequestContext $context) {
+    throw new \Exception();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getContext() {
+    throw new \Exception();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function generate($name, $parameters = array(), $referenceType = self::ABSOLUTE_PATH) {
+    throw new \Exception();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function generateFromPath($path = NULL, $options = array(), $collect_cacheability_metadata = FALSE) {
+    throw new \Exception();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPathFromRoute($name, $parameters = array()) {
+    throw new \Exception();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function generateFromRoute($name, $parameters = array(), $options = array(), $collect_cacheability_metadata = FALSE) {
+    throw new \Exception();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function supports($name) {
+    throw new \Exception();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRouteDebugMessage($name, array $parameters = array()) {
+    throw new \Exception();
+  }
+
+}