diff --git a/core/modules/serialization/tests/src/EntityResolver/UuidResolverTest.php b/core/modules/serialization/tests/src/EntityResolver/UuidResolverTest.php
index c41eea8..9d49dce 100644
--- a/core/modules/serialization/tests/src/EntityResolver/UuidResolverTest.php
+++ b/core/modules/serialization/tests/src/EntityResolver/UuidResolverTest.php
@@ -2,10 +2,10 @@
 
 /**
  * @file
- * Contains \Drupal\serialization\Tests\Normalizer\ListNormalizerTest.
+ * Contains \Drupal\serialization\Tests\EntityResolver\UuidResolverTest.
  */
 
-namespace Drupal\serialization\Tests\Normalizer;
+namespace Drupal\serialization\Tests\EntityResolver;
 
 use Drupal\Tests\UnitTestCase;
 use Drupal\serialization\EntityResolver\UuidResolver;
diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index 447fefc..1d70f35 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -435,14 +435,14 @@ function simpletest_log_read($test_id, $database_prefix, $test_class) {
  *   @endcode
  */
 function simpletest_test_get_all($module = NULL) {
-  return \Drupal::service('test_discovery')->find();
+  return \Drupal::service('test_discovery')->getTestClasses();
 }
 
 /**
  * Registers namespaces for disabled modules.
  */
 function simpletest_classloader_register() {
-  \Drupal::service('test_discovery')->registerTestClasses();
+  \Drupal::service('test_discovery')->registerTestNamespaces();
 }
 
 /**
diff --git a/core/modules/simpletest/src/TestDiscovery.php b/core/modules/simpletest/src/TestDiscovery.php
index f1b8ebc..f3f7fa9 100644
--- a/core/modules/simpletest/src/TestDiscovery.php
+++ b/core/modules/simpletest/src/TestDiscovery.php
@@ -17,18 +17,18 @@
 class TestDiscovery {
 
   /**
-   * Cached class map of all test classes discovered in extensions.
+   * Cached map of all test namespaces to respective directories.
    *
    * @var array
    */
-  protected static $classmap;
+  protected $testNamespaces;
 
   /**
-   * Cached list of all discovered tests.
+   * Cached list of all discovered test classes.
    *
    * @var array
    */
-  protected $allTests;
+  protected $testClasses;
 
   /**
    * Cached list of available extension names, keyed by extension type.
@@ -38,6 +38,61 @@ class TestDiscovery {
   protected $availableExtensions;
 
   /**
+   * Registers test namespaces of all available extensions.
+   *
+   * @return array
+   *   An associative array whose keys are PSR-4 namespace prefixes and whose
+   *   values are directory names.
+   *
+   * @todo Inject class loader.
+   */
+  public function registerTestNamespaces() {
+    if (isset($this->testNamespaces)) {
+      return $this->testNamespaces;
+    }
+    $this->testNamespaces = array();
+
+    $loader = drupal_classloader();
+    $existing = $loader->getPrefixes();
+    $old = array();
+    $new = array();
+
+    // Add PHPUnit test namespace of Drupal core.
+    $new['Drupal\\Tests\\'] = DRUPAL_ROOT . '/core/tests/Drupal/Tests';
+
+    $this->availableExtensions = array();
+    foreach ($this->getExtensions() as $name => $extension) {
+      $this->availableExtensions[$extension->getType()][$name] = $name;
+
+      $base_namespace = "Drupal\\$name\\";
+      $base_path = DRUPAL_ROOT . '/' . $extension->getPath();
+
+      // Add namespace of disabled/uninstalled extensions.
+      if (!isset($existing[$base_namespace])) {
+        $new[$base_namespace] = "$base_path/src";
+      }
+      else {
+        $old[$base_namespace] = reset($existing[$base_namespace]);
+      }
+      // Add PHPUnit test namespace.
+      // @todo Move PHPUnit namespace of extensions into Drupal\Tests\$name.
+      // @see https://drupal.org/node/2260121
+      $new[$base_namespace . 'Tests\\'] = "$base_path/tests/src";
+
+      // While being there, prime drupal_get_filename().
+      // @todo Remove this.
+      drupal_get_filename($extension->getType(), $name, $extension->getPathname());
+    }
+
+    foreach ($new as $prefix => $path) {
+      $loader->addPsr4($prefix, $path);
+    }
+
+    $this->testNamespaces = $new + $old;
+    return $this->testNamespaces;
+  }
+
+  /**
    * Discovers all available tests in all extensions.
    *
    * @return array
@@ -53,18 +108,12 @@ class TestDiscovery {
    *     );
    *   @endcode
    */
-  public function find() {
-    if (isset($this->allTests)) {
-      return $this->allTests;
+  public function getTestClasses() {
+    if (isset($this->testClasses)) {
+      return $this->testClasses;
     }
-    // Register test namespaces and test classes of all available extensions.
-    // (including disabled)
-    $classes = $this->registerTestClasses();
-
-    // Check that each class has a getInfo() method and store the information
-    // in an array keyed with the group specified in the test information.
-    $groups = array();
-    foreach ($classes as $classname => $pathname) {
+    $this->testClasses = array();
+    foreach ($this->findTestClasses() as $classname => $pathname) {
       try {
         $class = new \ReflectionClass($classname);
       }
@@ -83,7 +132,7 @@ public function find() {
       }
       $info = static::getTestInfo($class);
 
-      // If this test class requires a non-existing module, skip it.
+      // Skip this test class if it requires unavailable modules.
       if (!empty($info['requires']['module'])) {
         if (array_diff($info['requires']['module'], $this->availableExtensions['module'])) {
           continue;
@@ -94,20 +143,80 @@ public function find() {
       //   throws a PHPUnit_Framework_Warning exception.
       // @see simpletest_phpunit_get_available_tests()
 
-      $groups[$info['group']][$classname] = $info;
+      $this->testClasses[$info['group']][$classname] = $info;
     }
 
     // Sort the groups and tests within the groups by name.
-    uksort($groups, 'strnatcasecmp');
-    foreach ($groups as &$tests) {
+    uksort($this->testClasses, 'strnatcasecmp');
+    foreach ($this->testClasses as &$tests) {
       uksort($tests, 'strnatcasecmp');
     }
 
     // Allow modules extending core tests to disable originals.
-    \Drupal::moduleHandler()->alter('simpletest', $groups);
+    \Drupal::moduleHandler()->alter('simpletest', $this->testClasses);
 
-    $this->allTests = $groups;
-    return $groups;
+    return $this->testClasses;
+  }
+
+  /**
+   * Discovers all test classes in all available extensions.
+   *
+   * @return array
+   *   A classmap containing all discovered test classes.
+   */
+  protected function findTestClasses() {
+    $classmap = array();
+    foreach ($this->registerTestNamespaces() as $namespace => $path) {
+      if (!is_dir($path)) {
+        continue;
+      }
+      $classmap += static::scanDirectory($namespace, $path);
+    }
+    return $classmap;
+  }
+
+  /**
+   * Scans a given directory for class files.
+   *
+   * @param string $namespace_prefix
+   *   The namespace prefix to use for discovered classes. Must contain a
+   *   trailing namespace separator (backslash).
+   *   For example: 'Drupal\\node\\Tests\\'
+   * @param string $path
+   *   The directory path to scan.
+   *   For example: '/path/to/drupal/core/modules/node/tests/src'
+   *
+   * @return array
+   *   An associative array whose keys are fully-qualified class names and whose
+   *   values are corresponding filesystem pathnames.
+   */
+  public static function scanDirectory($namespace_prefix, $path) {
+    if (substr($namespace_prefix, -1) !== '\\') {
+      throw new \InvalidArgumentException("Namespace prefix for $path must contain a trailing namespace separator.");
+    }
+    $flags = \FilesystemIterator::UNIX_PATHS;
+    $flags |= \FilesystemIterator::SKIP_DOTS;
+    $flags |= \FilesystemIterator::FOLLOW_SYMLINKS;
+    $flags |= \FilesystemIterator::CURRENT_AS_SELF;
+
+    $iterator = new \RecursiveDirectoryIterator($path, $flags);
+    $filter = new \RecursiveCallbackFilterIterator($iterator, function ($current, $key, $iterator) {
+      if ($iterator->hasChildren()) {
+        return TRUE;
+      }
+      return $current->isFile() && $current->getExtension() === 'php';
+    });
+    $files = new \RecursiveIteratorIterator($filter);
+    $classes = array();
+    foreach ($files as $fileinfo) {
+      $class = $namespace_prefix;
+      if ('' !== $subpath = $fileinfo->getSubPath()) {
+        $class .= strtr($subpath, '/', '\\') . '\\';
+      }
+      $class .= $fileinfo->getBasename('.php');
+      $classes[$class] = $fileinfo->getPathname();
+    }
+    return $classes;
   }
 
   /**
@@ -240,144 +349,6 @@ public static function parseTestClassAnnotations(\ReflectionClass $class) {
   }
 
   /**
-   * Registers test classes for all available extensions.
-   *
-   * @return array
-   *   A classmap containing all discovered test classes, which has been added
-   *   to the classloader already.
-   *
-   * @see \Drupal\simpletest\TestDiscovery::getClassmap()
-   *
-   * @todo Inject class loader.
-   */
-  public function registerTestClasses() {
-    if (isset(static::$classmap)) {
-      return static::$classmap;
-    }
-    static::$classmap = array();
-    $this->availableExtensions = array();
-
-    $loader = drupal_classloader();
-    $existing = $loader->getPrefixes();
-
-    // Discover PHPUnit tests of core.
-    static::$classmap += static::scanDirectory(DRUPAL_ROOT . '/core/tests/Drupal/Tests', 'Drupal\\Tests\\');
-
-    // Safety net: Register PHPUnit test namespace.
-    // @todo Remove this; obsolete.
-    $loader->add('Drupal\\Tests', DRUPAL_ROOT . '/core/tests');
-
-    $extensions = $this->getExtensions();
-    foreach ($extensions as $name => $extension) {
-      $this->availableExtensions[$extension->getType()][$name] = $name;
-
-      $base_namespace = "Drupal\\$name\\";
-      $base_path = DRUPAL_ROOT . '/' . $extension->getPath();
-
-      // Register the namespace of disabled/uninstalled extensions.
-      if (!isset($existing[$base_namespace])) {
-        $loader->addPsr4($base_namespace, array(
-          "$base_path/lib/Drupal/$name",
-          "$base_path/src",
-        ));
-      }
-      // While being there, prime drupal_get_filename().
-      drupal_get_filename($extension->getType(), $name, $extension->getPathname());
-
-      // Discover all test classes and add them to the classmap.
-      $test_paths = array(
-        "$base_path/lib/Drupal/$name/Tests",
-        "$base_path/src/Tests",
-        "$base_path/tests/Drupal/$name/Tests",
-        "$base_path/tests/src",
-      );
-      $test_namespace = $base_namespace . 'Tests\\';
-      foreach ($test_paths as $test_path) {
-        if (!is_dir($test_path)) {
-          continue;
-        }
-        static::$classmap += static::scanDirectory($test_path, $test_namespace);
-      }
-
-      // Safety net: Register PHPUnit test namespace.
-      // @todo Remove this; obsolete.
-      $loader->addPsr4($base_namespace . 'Tests\\', array(
-        "$base_path/tests/Drupal/$name/Tests",
-        "$base_path/tests/src",
-      ));
-    }
-    $loader->addClassMap(static::$classmap);
-
-    return static::$classmap;
-  }
-
-  /**
-   * Scans a given directory for class files.
-   *
-   * @param string $path
-   *   The directory path to scan.
-   *   For example: '/path/to/drupal/core/modules/node/tests/src'
-   * @param string $namespace_prefix
-   *   The namespace prefix to use for discovered classes. Must contain a
-   *   trailing namespace separator (backslash).
-   *   For example: 'Drupal\\node\\Tests\\'
-   *
-   * @return array
-   *   An associative array whose keys are fully-qualified class names and whose
-   *   values are corresponding filesystem pathnames.
-   */
-  public static function scanDirectory($path, $namespace_prefix) {
-    if (substr($namespace_prefix, -1) !== '\\') {
-      throw new \InvalidArgumentException("Namespace prefix for $path must contain a trailing namespace separator.");
-    }
-    $flags = \FilesystemIterator::UNIX_PATHS;
-    $flags |= \FilesystemIterator::SKIP_DOTS;
-    $flags |= \FilesystemIterator::FOLLOW_SYMLINKS;
-    $flags |= \FilesystemIterator::CURRENT_AS_SELF;
-
-    $iterator = new \RecursiveDirectoryIterator($path, $flags);
-    $filter = new \RecursiveCallbackFilterIterator($iterator, function ($current, $key, $iterator) {
-      if ($iterator->hasChildren()) {
-        return TRUE;
-      }
-      return $current->isFile() && $current->getExtension() === 'php';
-    });
-    $files = new \RecursiveIteratorIterator($filter);
-    $classes = array();
-    foreach ($files as $fileinfo) {
-      $class = $namespace_prefix;
-      if ('' !== $subpath = $fileinfo->getSubPath()) {
-        $class .= strtr($subpath, '/', '\\') . '\\';
-      }
-      $class .= $fileinfo->getBasename('.php');
-      $classes[$class] = $fileinfo->getPathname();
-    }
-    return $classes;
-  }
-
-  /**
-   * Returns the previously discovered classmap, if any.
-   *
-   * @return array
-   */
-  public function getClassmap() {
-    return static::$classmap;
-  }
-
-  /**
-   * Sets the classmap.
-   *
-   * @param array $new_classmap
-   *   The new classmap.
-   *
-   * @return $this
-   */
-  public function setClassmap($new_classmap) {
-    static::$classmap = $new_classmap;
-    return $this;
-  }
-
-  /**
    * Returns all available extensions.
    *
    * @return \Drupal\Core\Extension\Extension[]
diff --git a/core/modules/system/src/Tests/Page/DefaultMetatagsTest.php b/core/modules/system/src/Tests/Page/DefaultMetatagsTest.php
index baae991..3b2afdf 100644
--- a/core/modules/system/src/Tests/Page/DefaultMetatagsTest.php
+++ b/core/modules/system/src/Tests/Page/DefaultMetatagsTest.php
@@ -9,6 +9,9 @@
 
 use Drupal\simpletest\WebTestBase;
 
+/**
+ * Tests default HTML metatags on a page.
+ */
 class DefaultMetatagsTest extends WebTestBase {
 
   /**
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index 88e9822..b99ef44 100755
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -11,7 +11,7 @@
 use Drupal\Core\Test\TestKernel;
 use Symfony\Component\HttpFoundation\Request;
 
-$loader = require_once __DIR__ . '/../vendor/autoload.php';
+require_once __DIR__ . '/../vendor/autoload.php';
 
 const SIMPLETEST_SCRIPT_COLOR_PASS = 32; // Green.
 const SIMPLETEST_SCRIPT_COLOR_FAIL = 31; // Red.
@@ -29,33 +29,12 @@
 simpletest_script_bootstrap();
 
 if ($args['execute-test']) {
-  // @todo A test classmap is actually unnecessary for running a single test.
-  //   Instead, an "extension map" would be much more effective, in order to
-  //   prime ExtensionDiscovery's static cache ahead of time.
-  //   Oh, and likewise InfoParser's.
-  $start = microtime(TRUE);
-  $classmap = json_decode(file_get_contents('test/test.classmap.json'), TRUE);
-  $loader->addClassMap($classmap);
-  simpletest_script_bootstrap();
-//  $loader = drupal_classloader();
-//  \Drupal::service('test_discovery')->setClassmap($classmap);
-  echo var_dump(microtime(TRUE) - $start), "\n";
-
   simpletest_script_setup_database();
   simpletest_script_run_one_test($args['test-id'], $args['execute-test']);
   // Sub-process exited already; this is just for clarity.
   exit;
 }
 
-if (!is_dir('./test')) {
-  mkdir('test', 0755);
-}
-$start = microtime(TRUE);
-simpletest_classloader_register();
-$classmap = \Drupal::service('test_discovery')->getClassmap();
-file_put_contents('test/test.classmap.json', json_encode($classmap, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES));
-echo var_dump(microtime(TRUE) - $start), "\n";
-
 simpletest_script_setup_database(TRUE);
 
 if ($args['clean']) {
@@ -416,6 +395,8 @@ function simpletest_script_bootstrap() {
 
   $module_handler = $container->get('module_handler');
   $module_handler->loadAll();
+
+  simpletest_classloader_register();
 }
 
 /**
diff --git a/core/tests/Drupal/Tests/Component/PhpStorage/FileStorageReadOnlyTest.php b/core/tests/Drupal/Tests/Component/PhpStorage/FileStorageReadOnlyTest.php
index 4d4bc0f..a907a07 100644
--- a/core/tests/Drupal/Tests/Component/PhpStorage/FileStorageReadOnlyTest.php
+++ b/core/tests/Drupal/Tests/Component/PhpStorage/FileStorageReadOnlyTest.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Contains \Drupal\Tests\Component\PhpStorage\FileStorageTest.
+ * Contains \Drupal\Tests\Component\PhpStorage\FileStorageReadOnlyTest.
  */
 
 namespace Drupal\Tests\Component\PhpStorage;
@@ -18,7 +18,7 @@
  *
  * @coversDefaultClass \Drupal\Component\PhpStorage\FileReadOnlyStorage
  */
-class FileStorageReadyOnlyTest extends PhpStorageTestBase {
+class FileStorageReadOnlyTest extends PhpStorageTestBase {
 
   /**
    * Standard test settings to pass to storage instances.
diff --git a/core/tests/Drupal/Tests/Core/Logger/LogMessageParserTest.php b/core/tests/Drupal/Tests/Core/Logger/LogMessageParserTest.php
index e30f551..2fa198e 100644
--- a/core/tests/Drupal/Tests/Core/Logger/LogMessageParserTest.php
+++ b/core/tests/Drupal/Tests/Core/Logger/LogMessageParserTest.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Contains \Drupal\Tests\Core\Logger\LogMessageParserTraitTest
+ * Contains \Drupal\Tests\Core\Logger\LogMessageParserTest.
  */
 
 namespace Drupal\Tests\Core\Logger;
diff --git a/core/tests/Drupal/Tests/Core/Logger/LoggerChannelFactoryTest.php b/core/tests/Drupal/Tests/Core/Logger/LoggerChannelFactoryTest.php
index 82e20b2..8bbe4ab 100644
--- a/core/tests/Drupal/Tests/Core/Logger/LoggerChannelFactoryTest.php
+++ b/core/tests/Drupal/Tests/Core/Logger/LoggerChannelFactoryTest.php
@@ -2,10 +2,10 @@
 
 /**
  * @file
- * Contains \Drupal\Tests\Core\Logger\LoggerChannelFactoryTest
+ * Contains \Drupal\Tests\Core\Logger\LoggerChannelFactoryTest.
  */
 
-namespace Drupal\Tests\Logger;
+namespace Drupal\Tests\Core\Logger;
 
 use Drupal\Core\Logger\LoggerChannelFactory;
 use Drupal\Core\Session\AccountInterface;
diff --git a/core/tests/Drupal/Tests/Core/Logger/LoggerChannelTest.php b/core/tests/Drupal/Tests/Core/Logger/LoggerChannelTest.php
index 2cc0a50..51c7e86 100644
--- a/core/tests/Drupal/Tests/Core/Logger/LoggerChannelTest.php
+++ b/core/tests/Drupal/Tests/Core/Logger/LoggerChannelTest.php
@@ -2,10 +2,10 @@
 
 /**
  * @file
- * Contains \Drupal\Tests\Core\Logger\LoggerChannelTest
+ * Contains \Drupal\Tests\Core\Logger\LoggerChannelTest.
  */
 
-namespace Drupal\Tests\Logger;
+namespace Drupal\Tests\Core\Logger;
 
 use Drupal\Core\Logger\LoggerChannel;
 use Drupal\Core\Session\AccountInterface;
diff --git a/core/tests/Drupal/Tests/Core/Path/AliasManagerTest.php b/core/tests/Drupal/Tests/Core/Path/AliasManagerTest.php
index f8d5c0e..bffc88d 100644
--- a/core/tests/Drupal/Tests/Core/Path/AliasManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Path/AliasManagerTest.php
@@ -2,10 +2,10 @@
 
 /**
  * @file
- * Contains \Drupal\Tests\Core\ExternalUrlTest.
+ * Contains \Drupal\Tests\Core\Path\AliasManagerTest.
  */
 
-namespace Drupal\Tests\Core;
+namespace Drupal\Tests\Core\Path;
 
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\Language\Language;