diff --git a/core/modules/simpletest/simpletest.api.php b/core/modules/simpletest/simpletest.api.php
index dad9a39..e5251b7 100644
--- a/core/modules/simpletest/simpletest.api.php
+++ b/core/modules/simpletest/simpletest.api.php
@@ -14,9 +14,9 @@
  * Alter the list of tests.
  *
  * @param $groups
- *   A two dimension array, the first key is the test group (as defined in
- *   getInfo) the second is the name of the class and the value is the return
- *   value of the getInfo method.
+ *   A two dimensional array, the first key is the test group, the second is the
+ *   name of the test class, and the value is in associative array containing
+ *   'name', 'description', 'group', and 'requires' keys.
  */
 function hook_simpletest_alter(&$groups) {
   // An alternative session handler module would not want to run the original
diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index 1d70f35..1654c3a 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -5,6 +5,7 @@
 use Drupal\Core\Extension\ExtensionDiscovery;
 use Drupal\Core\Render\Element;
 use Drupal\simpletest\TestBase;
+use Drupal\simpletest\TestDiscovery;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\Process\PhpExecutableFinder;
 
@@ -88,40 +89,34 @@ function _simpletest_format_summary_line($summary) {
  *
  * @param $test_list
  *   List of tests to run.
- * @param $reporter
- *   Which reporter to use. Allowed values are: text, xml, html and drupal,
- *   drupal being the default.
  *
  * @return string
  *   The test ID.
  */
-function simpletest_run_tests($test_list, $reporter = 'drupal') {
+function simpletest_run_tests($test_list) {
   $test_id = db_insert('simpletest_test_id')
     ->useDefaults(array('test_id'))
     ->execute();
 
-  $phpunit_tests = isset($test_list['UnitTest']) ? $test_list['UnitTest'] : array();
-  if ($phpunit_tests) {
+  if (!empty($test_list['phpunit'])) {
     $phpunit_results = simpletest_run_phpunit_tests($test_id, $phpunit_tests);
     simpletest_process_phpunit_results($phpunit_results);
   }
 
-  if (!array_key_exists('WebTest', $test_list) || empty($test_list['WebTest'])) {
-    // Early return if there are no WebTests to run.
+  // Early return if there are no further tests to run.
+  if (empty($test_list['simpletest'])) {
     return $test_id;
   }
 
-  // Contine with SimpleTests only.
-  $test_list = $test_list['WebTest'];
+  // Continue with SimpleTests only.
+  $test_list = $test_list['simpletest'];
 
   // Clear out the previous verbose files.
   file_unmanaged_delete_recursive('public://simpletest/verbose');
 
   // Get the info for the first test being run.
-  $first_test = array_shift($test_list);
-  $first_instance = new $first_test();
-  array_unshift($test_list, $first_test);
-  $info = $first_instance->getInfo();
+  $first_test = reset($test_list);
+  $info = TestDiscovery::getTestInfo(new \ReflectionClass($first_test));
 
   $batch = array(
     'title' => t('Running tests'),
@@ -295,7 +290,7 @@ function _simpletest_batch_operation($test_list_init, $test_id, &$context) {
   $test = new $test_class($test_id);
   $test->run();
   $size = count($test_list);
-  $info = $test->getInfo();
+  $info = TestDiscovery::getTestInfo(new \ReflectionClass($test));
 
   \Drupal::moduleHandler()->invokeAll('test_finished', array($test->results));
 
@@ -422,8 +417,8 @@ function simpletest_log_read($test_id, $database_prefix, $test_class) {
  *   returned.
  *
  * @return array[]
- *   An array of tests keyed with the groups specified in each of the tests'
- *   getInfo() methods and then keyed by the test classes. For example:
+ *   An array of tests keyed with the groups, and then keyed by test classes.
+ *   For example:
  *   @code
  *     $groups['Block'] => array(
  *       'BlockTestCase' => array(
@@ -603,59 +598,6 @@ function simpletest_mail_alter(&$message) {
 }
 
 /**
- * Gets PHPUnit classes.
- *
- * @param string $module
- *   Name of a module. If set then only tests belonging to this module is
- *   returned.
- *
- * @return array
- *   Returns an array of test classes.
- *
- * @throws \RuntimeException
- *   This is thrown when anything is wrong with a test.
- */
-function simpletest_phpunit_get_available_tests($module = NULL) {
-  // Try to load the class names array from cache.
-  $cid = 'simpletest_phpunit:' . $module;
-  if ($cache = \Drupal::cache()->get($cid)) {
-    $test_classes = $cache->data;
-  }
-  else {
-    if ($module) {
-      $prefix = 'Drupal\\' . $module . '\\';
-      $n = strlen($prefix);
-    }
-    // If there was no cached data available we have to find the tests.
-    // Load the PHPUnit configuration file, which tells us where to find the
-    // tests.
-    $phpunit_config = simpletest_phpunit_configuration_filepath();
-    $configuration = PHPUnit_Util_Configuration::getInstance($phpunit_config);
-    // Find all the tests and get a list of unique class names.
-    $test_suite = $configuration->getTestSuiteConfiguration(NULL);
-    $test_classes = array();
-    foreach ($test_suite as $test) {
-      // PHPUnit returns a warning message if something is wrong with a test,
-      // throw an exception to avoid an error when trying to call getInfo() on
-      // this.
-      if ($test instanceof PHPUnit_Framework_Warning) {
-        throw new RuntimeException($test->getMessage());
-      }
-
-      $name = get_class($test);
-      if (!array_key_exists($name, $test_classes) && (!$module || substr($name, 0, $n) == $prefix)) {
-        $test_classes[$name] = $test->getInfo();
-      }
-    }
-
-    // Since we have recalculated, we now need to store the new data into cache.
-    \Drupal::cache()->set($cid, $test_classes);
-  }
-
-  return $test_classes;
-}
-
-/**
  * Converts PHPUnit's JUnit XML output to an array.
  *
  * @param $test_id
diff --git a/core/modules/simpletest/src/Form/SimpletestTestForm.php b/core/modules/simpletest/src/Form/SimpletestTestForm.php
index ca84a43..a85f941 100644
--- a/core/modules/simpletest/src/Form/SimpletestTestForm.php
+++ b/core/modules/simpletest/src/Form/SimpletestTestForm.php
@@ -27,6 +27,20 @@ public function getFormId() {
    * {@inheritdoc}
    */
   public function buildForm(array $form, array &$form_state) {
+    $form['actions'] = array('#type' => 'actions');
+    $form['actions']['submit'] = array(
+      '#type' => 'submit',
+      '#value' => $this->t('Run tests'),
+      '#tableselect' => TRUE,
+      '#button_type' => 'primary',
+    );
+
+    // Do not needlessly re-execute a full test discovery if the user input
+    // already contains an explicit list of test classes to run.
+    if (!empty($form_state['input']['tests'])) {
+      return $form;
+    }
+
     // JavaScript-only table filters.
     $form['filters'] = array(
       '#type' => 'container',
@@ -96,8 +110,6 @@ public function buildForm(array $form, array &$form_state) {
 
     // Generate the list of tests arranged by group.
     $groups = simpletest_test_get_all();
-    $form_state['storage']['PHPUnit'] = $groups['PHPUnit'];
-
     foreach ($groups as $group => $tests) {
       $form['tests'][$group] = array(
         '#attributes' => array('class' => array('simpletest-group')),
@@ -158,15 +170,6 @@ public function buildForm(array $form, array &$form_state) {
       }
     }
 
-    // Action buttons.
-    $form['actions'] = array('#type' => 'actions');
-    $form['actions']['submit'] = array(
-      '#type' => 'submit',
-      '#value' => $this->t('Run tests'),
-      '#tableselect' => TRUE,
-      '#button_type' => 'primary',
-    );
-
     $form['clean'] = array(
       '#type' => 'fieldset',
       '#title' => $this->t('Clean test environment'),
@@ -186,16 +189,31 @@ public function buildForm(array $form, array &$form_state) {
    * {@inheritdoc}
    */
   public function submitForm(array &$form, array &$form_state) {
+    // Test discovery does not run upon form submission.
     simpletest_classloader_register();
 
-    $phpunit_all = $form_state['storage']['PHPUnit'];
+    // This form accepts arbitrary user input for 'tests'.
+    // An invalid value will cause the $class_name lookup below to die with a
+    // fatal error. Regular user access mechanisms to this form are intact.
+    // The only validation effectively being skipped is the validation of
+    // available checkboxes vs. submitted checkboxes.
+    // @todo Refactor Form API to allow to POST values without constructing the
+    //   entire form more easily, BUT retaining routing access security and
+    //   retaining Form API CSRF #token security validation, and without having
+    //   to rely on form caching.
+    if (empty($form_state['values']['tests']) && !empty($form_state['input']['tests'])) {
+      $form_state['values']['tests'] = $form_state['input']['tests'];
+    }
 
     $tests_list = array();
     foreach ($form_state['values']['tests'] as $class_name => $value) {
-      // Since class_exists() will likely trigger an autoload lookup,
-      // we do the fast check first.
-      if ($value === $class_name && class_exists($class_name)) {
-        $test_type = isset($phpunit_all[$class_name]) ? 'UnitTest' : 'WebTest';
+      if ($value === $class_name) {
+        if (is_subclass_of($class_name, 'PHPUnit_Framework_TestCase')) {
+          $test_type = 'phpunit';
+        }
+        else {
+          $test_type = 'simpletest';
+        }
         $tests_list[$test_type][] = $class_name;
       }
     }
diff --git a/core/modules/simpletest/src/TestDiscovery.php b/core/modules/simpletest/src/TestDiscovery.php
index 71e3025..dac7a43 100644
--- a/core/modules/simpletest/src/TestDiscovery.php
+++ b/core/modules/simpletest/src/TestDiscovery.php
@@ -9,6 +9,8 @@
 
 use Drupal\Core\Extension\Extension;
 use Drupal\Core\Extension\ExtensionDiscovery;
+use PHPUnit_Framework_TestSuite;
+use PHPUnit_Framework_Warning;
 use PHPUnit_Util_Test;
 
 /**
@@ -140,7 +142,8 @@ public function getTestClasses() {
         continue;
       }
       // Skip non-test classes.
-      if (!$class->isSubclassOf('Drupal\simpletest\TestBase') && !$class->isSubclassOf('PHPUnit_Framework_TestCase')) {
+      $phpunit = FALSE;
+      if (!$class->isSubclassOf('Drupal\simpletest\TestBase') && !$phpunit = $class->isSubclassOf('PHPUnit_Framework_TestCase')) {
         continue;
       }
       $info = static::getTestInfo($class);
@@ -154,10 +157,14 @@ public function getTestClasses() {
           continue;
         }
       }
-      // @todo Check whether PHPUnit's native validation is required. If so:
-      //   Construct a PHPUnit_Framework_TestSuite($class) and omit the test
-      //   class if that throws a PHPUnit_Framework_Warning exception.
-      // @see simpletest_phpunit_get_available_tests()
+      // @todo Check whether PHPUnit's native validation is really required.
+      if ($phpunit) {
+        $suite = new PHPUnit_Framework_TestSuite($class);
+        // PHPUnit returns a warning if something is wrong with a test.
+        if ($suite instanceof PHPUnit_Framework_Warning) {
+          throw new \RuntimeException($test->getMessage());
+        }
+      }
 
       $this->testClasses[$info['group']][$classname] = $info;
     }