diff --git a/core/lib/Drupal/Component/Plugin/CategorizingPluginManagerInterface.php b/core/lib/Drupal/Component/Plugin/CategorizingPluginManagerInterface.php
index 01f7eaf..bb9df77 100644
--- a/core/lib/Drupal/Component/Plugin/CategorizingPluginManagerInterface.php
+++ b/core/lib/Drupal/Component/Plugin/CategorizingPluginManagerInterface.php
@@ -32,7 +32,10 @@ public function getCategories();
   public function getSortedDefinitions(array $definitions = NULL);
 
   /**
-   * Gets definitions grouped by category.
+   * Gets sorted definitions grouped by category.
+   *
+   * In addition to grouping, both categories and its entries are sorted,
+   * whereas definitions are sorted by label.
    *
    * @param array[]|null $definitions
    *   (optional) The definitions to group. If omitted, all definitions are
diff --git a/core/lib/Drupal/Core/Block/BlockManager.php b/core/lib/Drupal/Core/Block/BlockManager.php
index f87485e..086016d 100644
--- a/core/lib/Drupal/Core/Block/BlockManager.php
+++ b/core/lib/Drupal/Core/Block/BlockManager.php
@@ -70,7 +70,7 @@ public function getSortedDefinitions(array $definitions = NULL) {
    * {@inheritdoc}
    */
   public function getGroupedDefinitions(array $definitions = NULL) {
-    $definitions = $this->traitGetGroupedDefinitions($definitions);
+    $definitions = $this->traitGetGroupedDefinitions($definitions, 'admin_label');
     // Do not display the 'broken' plugin in the UI.
     unset($definitions[$this->t('Block')]['broken']);
     return $definitions;
diff --git a/core/lib/Drupal/Core/Plugin/CategorizingPluginManagerTrait.php b/core/lib/Drupal/Core/Plugin/CategorizingPluginManagerTrait.php
index 4450deb..5a608e6 100644
--- a/core/lib/Drupal/Core/Plugin/CategorizingPluginManagerTrait.php
+++ b/core/lib/Drupal/Core/Plugin/CategorizingPluginManagerTrait.php
@@ -39,8 +39,10 @@
    *   The plugin definition.
    */
   protected function processDefinitionCategory(&$definition) {
-    // Ensure that every block has a category.
+    // Ensure that every plugin has a category.
     if (empty($definition['category'])) {
+      // Default to the human readable module name if the provider is a module;
+      // otherwise the provider machine name is used.
       $definition['category'] = $this->getModuleName($definition['provider']);
     }
   }
@@ -99,9 +101,9 @@ public function getSortedDefinitions(array $definitions = NULL, $label_key = 'la
   /**
    * Implements \Drupal\Component\Plugin\CategorizingPluginManagerInterface::getGroupedDefinitions().
    */
-  public function getGroupedDefinitions(array $definitions = NULL) {
+  public function getGroupedDefinitions(array $definitions = NULL, $label_key = 'label') {
     /** @var \Drupal\Core\Plugin\CategorizingPluginManagerTrait|\Drupal\Component\Plugin\PluginManagerInterface $this */
-    $definitions = isset($definitions) ? $definitions : $this->getDefinitions();
+    $definitions = $this->getSortedDefinitions(isset($definitions) ? $definitions : $this->getDefinitions(), $label_key);
     $grouped_definitions = array();
     foreach ($definitions as $id => $definition) {
       $grouped_definitions[$definition['category']][$id] = $definition;
diff --git a/core/tests/Drupal/Tests/Core/Plugin/CategorizingPluginManagerTraitTest.php b/core/tests/Drupal/Tests/Core/Plugin/CategorizingPluginManagerTraitTest.php
new file mode 100644
index 0000000..65703b6
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Plugin/CategorizingPluginManagerTraitTest.php
@@ -0,0 +1,151 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\Core\Plugin\CategorizingPluginManagerTraitTest.
+ */
+
+namespace Drupal\Tests\Core\Plugin {
+
+  use Drupal\Component\Plugin\CategorizingPluginManagerInterface;
+  use Drupal\Core\Plugin\CategorizingPluginManagerTrait;
+  use Drupal\Core\Plugin\DefaultPluginManager;
+  use Drupal\Tests\UnitTestCase;
+
+  /**
+   * @coversDefaultClass \Drupal\Core\Plugin\CategorizingPluginManagerTrait
+   * @group Plugin
+   */
+  class CategorizingPluginManagerTraitTest extends UnitTestCase {
+
+    /**
+     * The plugin manager to test.
+     *
+     * @var \Drupal\Component\Plugin\CategorizingPluginManagerInterface | \PHPUnit_Framework_MockObject_MockObject
+     */
+    protected $pluginManager;
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function setUp() {
+      $this->pluginManager = new CategorizingPluginManagerImpl();
+      $this->pluginManager->setStringTranslation($this->getStringTranslationStub());
+    }
+
+    /**
+     * @covers ::getCategories
+     */
+    public function testGetCategories() {
+      $this->assertSame(array_values($this->pluginManager->getCategories()), [
+          'fruits',
+          'vegetables'
+        ]);
+    }
+
+    /**
+     * @covers ::getSortedDefinitions
+     */
+    public function testGetSortedDefinitions() {
+      $sorted = $this->pluginManager->getSortedDefinitions();
+      $this->assertSame(array_keys($sorted), ['apple', 'mango', 'cucumber']);
+    }
+
+    /**
+     * @covers ::getGroupedDefinitions
+     */
+    public function testGetGroupedDefinitions() {
+      $grouped = $this->pluginManager->getGroupedDefinitions();
+      $this->assertSame(array_keys($grouped), ['fruits', 'vegetables']);
+      $this->assertSame(array_keys($grouped['fruits']), ['apple', 'mango']);
+      $this->assertSame(array_keys($grouped['vegetables']), ['cucumber']);
+    }
+
+    /**
+     * @covers ::processDefinitionCategory
+     */
+    public function testProcessDefinitionCategory() {
+      // Existing category.
+      $definition = array(
+        'label' => 'some',
+        'provider' => 'core',
+        'category' => 'bag',
+      );
+      $this->pluginManager->processDefinition($definition, 'some');
+      $this->assertSame($definition['category'], 'bag');
+
+      // No category, provider without label.
+      $definition = array(
+        'label' => 'some',
+        'provider' => 'core',
+      );
+      $this->pluginManager->processDefinition($definition, 'some');
+      $this->assertSame($definition['category'], 'core');
+
+      // No category, provider is module with label.
+      $definition = array(
+        'label' => 'some',
+        'provider' => 'node',
+      );
+      $this->pluginManager->processDefinition($definition, 'some');
+      $this->assertSame($definition['category'], 'Node');
+    }
+  }
+
+  /**
+   * Class that allows testing the trait.
+   */
+  class CategorizingPluginManagerImpl extends DefaultPluginManager implements CategorizingPluginManagerInterface {
+
+    use CategorizingPluginManagerTrait;
+
+    /**
+     * Replace the constructor so we can instantiate a stub.
+     */
+    public function __construct() {
+    }
+
+    /**
+     * Implements getDefinitions() for the trait to provide some test definitions.
+     *
+     * @return array
+     */
+    public function getDefinitions() {
+      return [
+        'cucumber' => array(
+          'label' => 'cucumber',
+          'category' => 'vegetables',
+        ),
+        'apple' => array(
+          'label' => 'apple',
+          'category' => 'fruits',
+        ),
+        'mango' => array(
+          'label' => 'mango',
+          'category' => 'fruits',
+        ),
+      ];
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function processDefinition(&$definition, $plugin_id) {
+      parent::processDefinition($definition, $plugin_id);
+      $this->processDefinitionCategory($definition);
+    }
+  }
+}
+
+namespace {
+
+  /**
+   * "Mocks" system_get_info() as needed for the test.
+   */
+  if (!function_exists('system_get_info')) {
+
+    function system_get_info($type, $name = NULL) {
+      return array('node' => array('name' => 'Node'));
+    }
+  }
+}