diff --git a/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestTestForm.php b/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestTestForm.php
index 18d7680..f79a3d8 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestTestForm.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/Form/SimpletestTestForm.php
@@ -82,10 +82,15 @@ public function buildForm(array $form, array &$form_state) {
       '#title' => $this->t('Collapse'),
       '#suffix' => '<a href="#" class="simpletest-collapse">(' . $this->t('Collapse') . ')</a>',
     );
-    $js = array(
-      'images' => array(
-        drupal_render($image_collapsed),
-        drupal_render($image_extended),
+    $form['tests']['#attached']['js'][] = array(
+      'type' => 'setting',
+      'data' => array(
+        'simpleTest' => array(
+          'images' => array(
+            drupal_render($image_collapsed),
+            drupal_render($image_extended),
+          ),
+        ),
       ),
     );
 
@@ -108,13 +113,13 @@ public function buildForm(array $form, array &$form_state) {
       $form['tests'][$group]['select'] = array(
         '#wrapper_attributes' => array(
           'id' => $group_class,
-          'class' => array('simpletest-select-all'),
+          'class' => array('simpletest-group-select-all'),
         ),
       );
       $form['tests'][$group]['title'] = array(
         // Expand/collapse image.
         '#prefix' => '<div class="simpletest-image" id="simpletest-test-group-' . $group_class . '"></div>',
-        '#markup' => '<label for="' . $group_class . '-select-all" class="simpletest-group-label">' . $group . '</label>',
+        '#markup' => '<label for="' . $group_class . '-group-select-all">' . $group . '</label>',
         '#wrapper_attributes' => array(
           'class' => array('simpletest-group-label'),
         ),
@@ -126,15 +131,6 @@ public function buildForm(array $form, array &$form_state) {
         ),
       );
 
-      // Add individual tests to group.
-      $current_js = array(
-        'testClass' => $group_class . '-test',
-        'testNames' => array(),
-        // imageDirection maps to the 'images' index in the $js array.
-        'imageDirection' => 0,
-        'clickActive' => FALSE,
-      );
-
       // Sort test classes within group alphabetically by name/label.
       uasort($tests, function ($a, $b) {
         return SortArray::sortByKeyString($a, $b, 'name');
@@ -144,7 +140,6 @@ public function buildForm(array $form, array &$form_state) {
       foreach ($tests as $class => $info) {
         $test_id = drupal_clean_id_identifier($class);
         $test_checkbox_id = 'edit-tests-' . $test_id;
-        $current_js['testNames'][] = $test_checkbox_id;
 
         $form['tests'][$class] = array(
           '#attributes' => array('class' => array($group_class . '-test', 'js-hide')),
@@ -168,16 +163,8 @@ public function buildForm(array $form, array &$form_state) {
           ),
         );
       }
-
-      $js['simpletest-test-group-' . $group_class] = $current_js;
     }
 
-    // Add JavaScript array of settings.
-    $form['tests']['#attached']['js'][] = array(
-      'type' => 'setting',
-      'data' => array('simpleTest' => $js),
-    );
-
     // Action buttons.
     $form['actions'] = array('#type' => 'actions');
     $form['actions']['submit'] = array(
diff --git a/core/modules/simpletest/simpletest.js b/core/modules/simpletest/simpletest.js
index ce79a0f..c8aa11b 100644
--- a/core/modules/simpletest/simpletest.js
+++ b/core/modules/simpletest/simpletest.js
@@ -3,98 +3,62 @@
   "use strict";
 
   /**
-   * Add the cool table collapsing on the testing overview page.
+   * Collapses table rows followed by group rows on the test listing page.
    */
-  Drupal.behaviors.simpleTestMenuCollapse = {
+  Drupal.behaviors.simpleTestGroupCollapse = {
     attach: function (context) {
-      var timeout = null;
-      // Adds expand-collapse functionality.
-      $('div.simpletest-image').once('simpletest-image', function () {
-        var $this = $(this);
-        var direction = drupalSettings.simpleTest[this.id].imageDirection;
-        $this.html(drupalSettings.simpleTest.images[direction]);
-
-        // Adds group toggling functionality to arrow images.
-        $this.on('click', function () {
-          var trs = $this.closest('tbody').children('.' + drupalSettings.simpleTest[this.id].testClass);
-          var direction = drupalSettings.simpleTest[this.id].imageDirection;
-          var row = direction ? trs.length - 1 : 0;
-
-          // If clicked in the middle of expanding a group, stop so we can switch directions.
-          if (timeout) {
-            clearTimeout(timeout);
-          }
-
-          // Function to toggle an individual row according to the current direction.
-          // We set a timeout of 20 ms until the next row will be shown/hidden to
-          // create a sliding effect.
-          function rowToggle() {
-            if (direction) {
-              if (row >= 0) {
-                $(trs[row]).hide();
-                row--;
-                timeout = setTimeout(rowToggle, 20);
-              }
+      $(context).find('.simpletest-group').once('simpletest-group-collapse', function () {
+        var $group = $(this);
+        var $image = $group.find('.simpletest-image');
+        $image
+          .html(drupalSettings.simpleTest.images[0])
+          .on('click', function () {
+            var $tests = $group.nextUntil('.simpletest-group');
+            if ($group.hasClass('expanded')) {
+              $group.removeClass('expanded');
+              $tests.addClass('js-hide');
+              $image.html(drupalSettings.simpleTest.images[0]);
             }
             else {
-              if (row < trs.length) {
-                $(trs[row]).removeClass('js-hide').show();
-                row++;
-                timeout = setTimeout(rowToggle, 20);
-              }
+              $group.addClass('expanded');
+              $tests.removeClass('js-hide');
+              $image.html(drupalSettings.simpleTest.images[1]);
             }
-          }
-
-          // Kick-off the toggling upon a new click.
-          rowToggle();
-
-          // Toggle the arrow image next to the test group title.
-          $this.html(drupalSettings.simpleTest.images[(direction ? 0 : 1)]);
-          drupalSettings.simpleTest[this.id].imageDirection = !direction;
-
-        });
+          });
       });
     }
   };
 
   /**
-   * Select/deselect all the inner checkboxes when the outer checkboxes are
-   * selected/deselected.
+   * Toggles test checkboxes to match the group checkbox.
    */
   Drupal.behaviors.simpleTestSelectAll = {
     attach: function (context) {
-      $('td.simpletest-select-all').once('simpletest-select-all', function () {
-        var testCheckboxes = drupalSettings.simpleTest['simpletest-test-group-' + $(this).attr('id')].testNames;
-        var groupCheckbox = $('<input type="checkbox" class="form-checkbox" id="' + $(this).attr('id') + '-select-all" />');
-
-        // Each time a single-test checkbox is checked or unchecked, make sure
-        // that the associated group checkbox gets the right state too.
-        function updateGroupCheckbox() {
-          var checkedTests = 0;
-          for (var i = 0; i < testCheckboxes.length; i++) {
-            if ($('#' + testCheckboxes[i]).prop('checked')) {
-              checkedTests++;
-            }
-          }
-          $(groupCheckbox).prop('checked', (checkedTests === testCheckboxes.length));
-        }
-
-        // Have the single-test checkboxes follow the group checkbox.
-        groupCheckbox.on('change', function () {
+      $(context).find('.simpletest-group').once('simpletest-group-select-all', function () {
+        var $group = $(this);
+        var $cell = $group.find('.simpletest-group-select-all');
+        var $groupCheckbox = $('<input type="checkbox" id="' + $cell.attr('id') + '-group-select-all" class="form-checkbox" />');
+        var $testCheckboxes = $group.nextUntil('.simpletest-group').find('input[type=checkbox]');
+        $cell.append($groupCheckbox);
+
+        // Toggle the test checkboxes when the group checkbox is toggled.
+        $groupCheckbox.on('change', function () {
           var checked = $(this).prop('checked');
-          for (var i = 0; i < testCheckboxes.length; i++) {
-            $('#' + testCheckboxes[i]).prop('checked', checked);
-          }
+          $testCheckboxes.prop('checked', checked);
         });
 
-        // Have the group checkbox follow the single-test checkboxes.
-        for (var i = 0; i < testCheckboxes.length; i++) {
-          $('#' + testCheckboxes[i]).on('change', updateGroupCheckbox);
+        // Update the group checkbox when a test checkbox is toggled.
+        function updateGroupCheckbox() {
+          var allChecked = true;
+          $testCheckboxes.each(function () {
+            if (!$(this).prop('checked')) {
+              allChecked = false;
+              return false;
+            }
+          });
+          $groupCheckbox.prop('checked', allChecked);
         }
-
-        // Initialize status for the group checkbox correctly.
-        updateGroupCheckbox();
-        $(this).append(groupCheckbox);
+        $testCheckboxes.on('change', updateGroupCheckbox);
       });
     }
   };
@@ -102,9 +66,6 @@
   /**
    * Filters the test list table by a text input search string.
    *
-   * Additionally accounts for multiple tables being wrapped in "package" details
-   * elements.
-   *
    * Text search input: input.table-filter-text
    * Target table:      input.table-filter-text[data-table]
    * Source text:       .table-filter-text-source
@@ -139,14 +100,8 @@
         else if (searched) {
           searched = false;
           $('#simpletest-form-table thead th.select-all input').show();
-          // Hide all rows and then show groups.
-          $rows.hide();
-          $rows.filter('.simpletest-group').show().each(function () {
-            var id = 'simpletest-test-group-' + $(this).children().first().attr('id');
-            if (drupalSettings.simpleTest[id].imageDirection) {
-              $(this).closest('tbody').children('.' + drupalSettings.simpleTest[id].testClass).show();
-            }
-          });
+          // Restore all rows to their original display state.
+          $rows.css('display', '');
         }
       }