diff --git a/core/lib/Drupal/Core/Test/TestRunnerKernel.php b/core/lib/Drupal/Core/Test/TestRunnerKernel.php
index 963a6c4e4d..f5b2ffb357 100644
--- a/core/lib/Drupal/Core/Test/TestRunnerKernel.php
+++ b/core/lib/Drupal/Core/Test/TestRunnerKernel.php
@@ -39,7 +39,7 @@ public function __construct($environment, $class_loader, $allow_dumping = FALSE,
     ];
     $this->moduleData = [
       'system' => new Extension($this->root, 'module', 'core/modules/system/system.info.yml', 'system.module'),
-      'simpletest' => new Extension($this->root, 'module', 'core/modules/simpletest/simpletest.info.yml', 'simpletest.module'),
+      'simpletest' => new Extension($this->root, 'module', 'core/modules/simpletest/simpletest.info.yml'),
     ];
   }
 
diff --git a/core/modules/simpletest/simpletest.info.yml b/core/modules/simpletest/simpletest.info.yml
new file mode 100644
index 0000000000..232680e7cf
--- /dev/null
+++ b/core/modules/simpletest/simpletest.info.yml
@@ -0,0 +1,7 @@
+name: Testing
+type: module
+description: 'Provides a framework for unit and functional testing.'
+package: Core
+version: VERSION
+core: 8.x
+configure: simpletest.settings
diff --git a/core/modules/simpletest/simpletest.services.yml b/core/modules/simpletest/simpletest.services.yml
new file mode 100644
index 0000000000..427947eaee
--- /dev/null
+++ b/core/modules/simpletest/simpletest.services.yml
@@ -0,0 +1,6 @@
+services:
+  test_discovery:
+    # @todo This class is deprecated. We use it here to support the deprecated
+    #   testing hooks. Remove this before Drupal 9.
+    class: Drupal\simpletest\TestDiscovery
+    arguments: ['@app.root', '@class_loader', '@module_handler']
diff --git a/core/modules/simpletest/src/TestDiscovery.php b/core/modules/simpletest/src/TestDiscovery.php
new file mode 100644
index 0000000000..8ce8b7de46
--- /dev/null
+++ b/core/modules/simpletest/src/TestDiscovery.php
@@ -0,0 +1,150 @@
+<?php
+
+namespace Drupal\simpletest;
+
+@trigger_error(__NAMESPACE__ . '\\TestDiscovery is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Use \Drupal\Core\Test\TestDiscovery instead. See https://www.drupal.org/node/2949692', E_USER_DEPRECATED);
+
+use Doctrine\Common\Reflection\StaticReflectionParser;
+use Drupal\Component\Annotation\Reflection\MockFileFinder;
+use Drupal\Component\Utility\NestedArray;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Test\Exception\MissingGroupException;
+use Drupal\Core\Test\TestDiscovery as CoreTestDiscovery;
+
+/**
+ * Discovers available tests.
+ *
+ * This class provides backwards compatibility for code which uses the legacy
+ * \Drupal\simpletest\TestDiscovery.
+ *
+ * @deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Use
+ *   \Drupal\Core\Test\TestDiscovery instead.
+ *
+ * @see https://www.drupal.org/node/2949692
+ */
+class TestDiscovery extends CoreTestDiscovery {
+
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface
+   */
+  protected $moduleHandler;
+
+  /**
+   * Constructs a new test discovery.
+   *
+   * @param string $root
+   *   The app root.
+   * @param $class_loader
+   *   The class loader. Normally Composer's ClassLoader, as included by the
+   *   front controller, but may also be decorated; e.g.,
+   *   \Symfony\Component\ClassLoader\ApcClassLoader.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler.
+   */
+  public function __construct($root, $class_loader, ModuleHandlerInterface $module_handler) {
+    parent::__construct($root, $class_loader);
+    $this->moduleHandler = $module_handler;
+  }
+
+  /**
+   * Discovers all available tests in all extensions.
+   *
+   * This method is a near-duplicate of
+   * \Drupal\Core\Tests\TestDiscovery::getTestClasses(). It exists so that we
+   * can provide a BC invocation of hook_simpletest_alter().
+   *
+   * @param string $extension
+   *   (optional) The name of an extension to limit discovery to; e.g., 'node'.
+   * @param string[] $types
+   *   An array of included test types.
+   *
+   * @return array
+   *   An array of tests keyed by the the group name. If a test is annotated to
+   *   belong to multiple groups, it will appear under all group keys it belongs
+   *   to.
+   * @code
+   *     $groups['block'] => array(
+   *       'Drupal\Tests\block\Functional\BlockTest' => array(
+   *         'name' => 'Drupal\Tests\block\Functional\BlockTest',
+   *         'description' => 'Tests block UI CRUD functionality.',
+   *         'group' => 'block',
+   *         'groups' => ['block', 'group2', 'group3'],
+   *       ),
+   *     );
+   * @endcode
+   */
+  public function getTestClasses($extension = NULL, array $types = []) {
+    if (!isset($extension) && empty($types)) {
+      if (!empty($this->testClasses)) {
+        return $this->testClasses;
+      }
+    }
+    $list = [];
+
+    $classmap = $this->findAllClassFiles($extension);
+
+    // Prevent expensive class loader lookups for each reflected test class by
+    // registering the complete classmap of test classes to the class loader.
+    // This also ensures that test classes are loaded from the discovered
+    // pathnames; a namespace/classname mismatch will throw an exception.
+    $this->classLoader->addClassMap($classmap);
+
+    foreach ($classmap as $classname => $pathname) {
+      $finder = MockFileFinder::create($pathname);
+      $parser = new StaticReflectionParser($classname, $finder, TRUE);
+      try {
+        $info = static::getTestInfo($classname, $parser->getDocComment());
+      }
+      catch (MissingGroupException $e) {
+        // If the class name ends in Test and is not a migrate table dump.
+        if (preg_match('/Test$/', $classname) && strpos($classname, 'migrate_drupal\Tests\Table') === FALSE) {
+          throw $e;
+        }
+        // If the class is @group annotation just skip it. Most likely it is an
+        // abstract class, trait or test fixture.
+        continue;
+      }
+      // Skip this test class if it is a Simpletest-based test and requires
+      // unavailable modules. TestDiscovery should not filter out module
+      // requirements for PHPUnit-based test classes.
+      // @todo Move this behavior to \Drupal\simpletest\TestBase so tests can be
+      //       marked as skipped, instead.
+      // @see https://www.drupal.org/node/1273478
+      if ($info['type'] == 'Simpletest') {
+        if (!empty($info['requires']['module'])) {
+          if (array_diff($info['requires']['module'], $this->availableExtensions['module'])) {
+            continue;
+          }
+        }
+      }
+
+      foreach ($info['groups'] as $group) {
+        $list[$group][$classname] = $info;
+      }
+    }
+
+    // Sort the groups and tests within the groups by name.
+    uksort($list, 'strnatcasecmp');
+    foreach ($list as &$tests) {
+      uksort($tests, 'strnatcasecmp');
+    }
+
+    // Allow modules extending core tests to disable originals.
+    $this->moduleHandler->alterDeprecated('Convert your test to a PHPUnit-based one and implement test listeners. See: https://www.drupal.org/node/2939892', 'simpletest', $list);
+
+    if (!isset($extension) && empty($types)) {
+      $this->testClasses = $list;
+    }
+
+    if ($types) {
+      $list = NestedArray::filter($list, function ($element) use ($types) {
+        return !(is_array($element) && isset($element['type']) && !in_array($element['type'], $types));
+      });
+    }
+
+    return $list;
+  }
+
+}