diff --git a/core/core.services.yml b/core/core.services.yml
index 70c6441f91e..0e7eb586e93 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -577,9 +577,6 @@ services:
   entity.autocomplete_matcher:
     class: Drupal\Core\Entity\EntityAutocompleteMatcher
     arguments: ['@plugin.manager.entity_reference_selection']
-  plugin_form.factory:
-    class: Drupal\Core\Plugin\PluginFormFactory
-    arguments: ['@class_resolver']
   plugin.manager.entity_reference_selection:
     class: Drupal\Core\Entity\EntityReferenceSelection\SelectionPluginManager
     parent: default_plugin_manager
diff --git a/core/lib/Drupal/Component/Plugin/PluginAwareInterface.php b/core/lib/Drupal/Component/Plugin/PluginAwareInterface.php
deleted file mode 100644
index 5506c9f7ab9..00000000000
--- a/core/lib/Drupal/Component/Plugin/PluginAwareInterface.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php
-
-namespace Drupal\Component\Plugin;
-
-/**
- * Provides an interface for objects that depend on a plugin.
- */
-interface PluginAwareInterface {
-
-  /**
-   * Sets the plugin for this object.
-   *
-   * @param \Drupal\Component\Plugin\PluginInspectionInterface $plugin
-   *   The plugin.
-   */
-  public function setPlugin(PluginInspectionInterface $plugin);
-
-}
diff --git a/core/lib/Drupal/Core/Block/BlockBase.php b/core/lib/Drupal/Core/Block/BlockBase.php
index bcc3954ae69..03d76acb663 100644
--- a/core/lib/Drupal/Core/Block/BlockBase.php
+++ b/core/lib/Drupal/Core/Block/BlockBase.php
@@ -10,7 +10,6 @@ use Drupal\Core\Plugin\ContextAwarePluginBase;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Language\LanguageInterface;
-use Drupal\Core\Plugin\PluginWithFormsInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Component\Transliteration\TransliterationInterface;
 
@@ -23,7 +22,7 @@ use Drupal\Component\Transliteration\TransliterationInterface;
  *
  * @ingroup block_api
  */
-abstract class BlockBase extends ContextAwarePluginBase implements BlockPluginInterface, PluginWithFormsInterface {
+abstract class BlockBase extends ContextAwarePluginBase implements BlockPluginInterface {
 
   use ContextAwarePluginAssignmentTrait;
 
@@ -272,20 +271,4 @@ abstract class BlockBase extends ContextAwarePluginBase implements BlockPluginIn
     $this->transliteration = $transliteration;
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function getFormClass($operation) {
-    if ($this->hasFormClass($operation)) {
-      return $this->getPluginDefinition()['forms'][$operation];
-    }
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function hasFormClass($operation) {
-    return isset($this->getPluginDefinition()['forms'][$operation]);
-  }
-
 }
diff --git a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
index fa706a47adc..06365fa0da0 100644
--- a/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
+++ b/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
@@ -239,20 +239,9 @@ class DefaultPluginManager extends PluginManagerBase implements PluginManagerInt
    * method.
    */
   public function processDefinition(&$definition, $plugin_id) {
-    // Only arrays can be operated on.
-    if (!is_array($definition)) {
-      return;
-    }
-
     if (!empty($this->defaults) && is_array($this->defaults)) {
       $definition = NestedArray::mergeDeep($this->defaults, $definition);
     }
-
-    // If no default form is defined and this plugin implements
-    // \Drupal\Core\Plugin\PluginFormInterface, use that for the default form.
-    if (!isset($definition['forms']['configure']) && isset($definition['class']) && is_subclass_of($definition['class'], PluginFormInterface::class)) {
-      $definition['forms']['configure'] = $definition['class'];
-    }
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Plugin/PluginFormBase.php b/core/lib/Drupal/Core/Plugin/PluginFormBase.php
deleted file mode 100644
index d0fe1b4026e..00000000000
--- a/core/lib/Drupal/Core/Plugin/PluginFormBase.php
+++ /dev/null
@@ -1,38 +0,0 @@
-<?php
-
-namespace Drupal\Core\Plugin;
-
-use Drupal\Component\Plugin\PluginAwareInterface;
-use Drupal\Component\Plugin\PluginInspectionInterface;
-use Drupal\Core\Form\FormStateInterface;
-
-/**
- * Provides a base class for plugin forms.
- *
- * Classes extending this can be in any namespace, but are commonly placed in
- * the 'PluginForm' namespace, such as \Drupal\module_name\PluginForm\ClassName.
- */
-abstract class PluginFormBase implements PluginFormInterface, PluginAwareInterface {
-
-  /**
-   * The plugin this form is for.
-   *
-   * @var \Drupal\Component\Plugin\PluginInspectionInterface
-   */
-  protected $plugin;
-
-  /**
-   * {@inheritdoc}
-   */
-  public function setPlugin(PluginInspectionInterface $plugin) {
-    $this->plugin = $plugin;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
-    // Validation is optional.
-  }
-
-}
diff --git a/core/lib/Drupal/Core/Plugin/PluginFormFactory.php b/core/lib/Drupal/Core/Plugin/PluginFormFactory.php
deleted file mode 100644
index 6cbbc22c763..00000000000
--- a/core/lib/Drupal/Core/Plugin/PluginFormFactory.php
+++ /dev/null
@@ -1,67 +0,0 @@
-<?php
-
-namespace Drupal\Core\Plugin;
-
-use Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException;
-use Drupal\Component\Plugin\PluginAwareInterface;
-use Drupal\Core\DependencyInjection\ClassResolverInterface;
-
-/**
- * Provides form discovery capabilities for plugins.
- */
-class PluginFormFactory implements PluginFormFactoryInterface {
-
-  /**
-   * The class resolver.
-   *
-   * @var \Drupal\Core\DependencyInjection\ClassResolverInterface
-   */
-  protected $classResolver;
-
-  /**
-   * PluginFormFactory constructor.
-   *
-   * @param \Drupal\Core\DependencyInjection\ClassResolverInterface $class_resolver
-   *   The class resolver.
-   */
-  public function __construct(ClassResolverInterface $class_resolver) {
-    $this->classResolver = $class_resolver;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function createInstance(PluginWithFormsInterface $plugin, $operation, $fallback_operation = NULL) {
-    if (!$plugin->hasFormClass($operation)) {
-      // Use the default form class if no form is specified for this operation.
-      if ($fallback_operation && $plugin->hasFormClass($fallback_operation)) {
-        $operation = $fallback_operation;
-      }
-      else {
-        throw new InvalidPluginDefinitionException($plugin->getPluginId(), sprintf('The "%s" plugin did not specify a "%s" form class', $plugin->getPluginId(), $operation));
-      }
-    }
-
-    $form_class = $plugin->getFormClass($operation);
-
-    // If the form specified is the plugin itself, use it directly.
-    if (ltrim(get_class($plugin), '\\') === ltrim($form_class, '\\')) {
-      $form_object = $plugin;
-    }
-    else {
-      $form_object = $this->classResolver->getInstanceFromDefinition($form_class);
-    }
-
-    // Ensure the resulting object is a plugin form.
-    if (!$form_object instanceof PluginFormInterface) {
-      throw new InvalidPluginDefinitionException($plugin->getPluginId(), sprintf('The "%s" plugin did not specify a valid "%s" form class, must implement \Drupal\Core\Plugin\PluginFormInterface', $plugin->getPluginId(), $operation));
-    }
-
-    if ($form_object instanceof PluginAwareInterface) {
-      $form_object->setPlugin($plugin);
-    }
-
-    return $form_object;
-  }
-
-}
diff --git a/core/lib/Drupal/Core/Plugin/PluginFormFactoryInterface.php b/core/lib/Drupal/Core/Plugin/PluginFormFactoryInterface.php
deleted file mode 100644
index 31679de2693..00000000000
--- a/core/lib/Drupal/Core/Plugin/PluginFormFactoryInterface.php
+++ /dev/null
@@ -1,34 +0,0 @@
-<?php
-
-namespace Drupal\Core\Plugin;
-
-
-/**
- * Provides an interface for retrieving form objects for plugins.
- *
- * This allows a plugin to define multiple forms, in addition to the plugin
- * itself providing a form. All forms, decoupled or self-contained, must
- * implement \Drupal\Core\Plugin\PluginFormInterface. Decoupled forms can
- * implement \Drupal\Component\Plugin\PluginAwareInterface in order to gain
- * access to the plugin.
- */
-interface PluginFormFactoryInterface {
-
-  /**
-   * Creates a new form instance.
-   *
-   * @param \Drupal\Core\Plugin\PluginWithFormsInterface $plugin
-   *   The plugin the form is for.
-   * @param string $operation
-   *   The name of the operation to use, e.g., 'add' or 'edit'.
-   * @param string $fallback_operation
-   *   (optional) The name of the fallback operation to use.
-   *
-   * @return \Drupal\Core\Plugin\PluginFormInterface
-   *   A plugin form instance.
-   *
-   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
-   */
-  public function createInstance(PluginWithFormsInterface $plugin, $operation, $fallback_operation = NULL);
-
-}
diff --git a/core/lib/Drupal/Core/Plugin/PluginFormInterface.php b/core/lib/Drupal/Core/Plugin/PluginFormInterface.php
index 397c98f0863..577735f1371 100644
--- a/core/lib/Drupal/Core/Plugin/PluginFormInterface.php
+++ b/core/lib/Drupal/Core/Plugin/PluginFormInterface.php
@@ -7,10 +7,6 @@ use Drupal\Core\Form\FormStateInterface;
 /**
  * Provides an interface for an embeddable plugin form.
  *
- * Plugins can implement this form directly, or a standalone class can be used.
- * Decoupled forms can implement \Drupal\Component\Plugin\PluginAwareInterface
- * in order to gain access to the plugin.
- *
  * @ingroup plugin_api
  */
 interface PluginFormInterface {
diff --git a/core/lib/Drupal/Core/Plugin/PluginWithFormsInterface.php b/core/lib/Drupal/Core/Plugin/PluginWithFormsInterface.php
deleted file mode 100644
index aed5adf4d2e..00000000000
--- a/core/lib/Drupal/Core/Plugin/PluginWithFormsInterface.php
+++ /dev/null
@@ -1,37 +0,0 @@
-<?php
-
-namespace Drupal\Core\Plugin;
-
-use Drupal\Component\Plugin\PluginInspectionInterface;
-
-/**
- * Provides an interface for plugins which have forms.
- *
- * Plugin forms are embeddable forms referenced by the plugin annotation.
- * Used by plugin types which have a larger number of plugin-specific forms.
- */
-interface PluginWithFormsInterface extends PluginInspectionInterface {
-
-  /**
-   * Gets the form class for the given operation.
-   *
-   * @param string $operation
-   *   The name of the operation.
-   *
-   * @return string|null
-   *   The form class if defined, NULL otherwise.
-   */
-  public function getFormClass($operation);
-
-  /**
-   * Gets whether the plugin has a form class for the given operation.
-   *
-   * @param string $operation
-   *   The name of the operation.
-   *
-   * @return bool
-   *   TRUE if the plugin has a form class for the given operation.
-   */
-  public function hasFormClass($operation);
-
-}
diff --git a/core/modules/block/src/BlockForm.php b/core/modules/block/src/BlockForm.php
index 03448b9abc9..eeec4d3338a 100644
--- a/core/modules/block/src/BlockForm.php
+++ b/core/modules/block/src/BlockForm.php
@@ -3,8 +3,6 @@
 namespace Drupal\block;
 
 use Drupal\Component\Utility\Html;
-use Drupal\Core\Plugin\PluginFormFactoryInterface;
-use Drupal\Core\Block\BlockPluginInterface;
 use Drupal\Core\Entity\EntityForm;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Executable\ExecutableManagerInterface;
@@ -70,13 +68,6 @@ class BlockForm extends EntityForm {
    */
   protected $contextRepository;
 
-  /**
-   * The plugin form manager.
-   *
-   * @var \Drupal\Core\Plugin\PluginFormFactoryInterface
-   */
-  protected $pluginFormFactory;
-
   /**
    * Constructs a BlockForm object.
    *
@@ -90,16 +81,13 @@ class BlockForm extends EntityForm {
    *   The language manager.
    * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
    *   The theme handler.
-   * @param \Drupal\Core\Plugin\PluginFormFactoryInterface $plugin_form_manager
-   *   The plugin form manager.
    */
-  public function __construct(EntityManagerInterface $entity_manager, ExecutableManagerInterface $manager, ContextRepositoryInterface $context_repository, LanguageManagerInterface $language, ThemeHandlerInterface $theme_handler, PluginFormFactoryInterface $plugin_form_manager) {
+  public function __construct(EntityManagerInterface $entity_manager, ExecutableManagerInterface $manager, ContextRepositoryInterface $context_repository, LanguageManagerInterface $language, ThemeHandlerInterface $theme_handler) {
     $this->storage = $entity_manager->getStorage('block');
     $this->manager = $manager;
     $this->contextRepository = $context_repository;
     $this->language = $language;
     $this->themeHandler = $theme_handler;
-    $this->pluginFormFactory = $plugin_form_manager;
   }
 
   /**
@@ -111,8 +99,7 @@ class BlockForm extends EntityForm {
       $container->get('plugin.manager.condition'),
       $container->get('context.repository'),
       $container->get('language_manager'),
-      $container->get('theme_handler'),
-      $container->get('plugin_form.factory')
+      $container->get('theme_handler')
     );
   }
 
@@ -133,7 +120,7 @@ class BlockForm extends EntityForm {
     $form_state->setTemporaryValue('gathered_contexts', $this->contextRepository->getAvailableContexts());
 
     $form['#tree'] = TRUE;
-    $form['settings'] = $this->getPluginForm($entity->getPlugin())->buildConfigurationForm(array(), $form_state);
+    $form['settings'] = $entity->getPlugin()->buildConfigurationForm(array(), $form_state);
     $form['visibility'] = $this->buildVisibilityInterface([], $form_state);
 
     // If creating a new block, calculate a safe default machine name.
@@ -295,7 +282,7 @@ class BlockForm extends EntityForm {
     // settings form element, so just pass that to the block for validation.
     $settings = (new FormState())->setValues($form_state->getValue('settings'));
     // Call the plugin validate handler.
-    $this->getPluginForm($this->entity->getPlugin())->validateConfigurationForm($form, $settings);
+    $this->entity->getPlugin()->validateConfigurationForm($form, $settings);
     // Update the original form values.
     $form_state->setValue('settings', $settings->getValues());
     $this->validateVisibility($form, $form_state);
@@ -342,8 +329,8 @@ class BlockForm extends EntityForm {
     $settings = (new FormState())->setValues($form_state->getValue('settings'));
 
     // Call the plugin submit handler.
+    $entity->getPlugin()->submitConfigurationForm($form, $settings);
     $block = $entity->getPlugin();
-    $this->getPluginForm($block)->submitConfigurationForm($form, $settings);
     // If this block is context-aware, set the context mapping.
     if ($block instanceof ContextAwarePluginInterface && $block->getContextDefinitions()) {
       $context_mapping = $settings->getValue('context_mapping', []);
@@ -415,17 +402,4 @@ class BlockForm extends EntityForm {
     return $machine_default;
   }
 
-  /**
-   * Retrieves the plugin form for a given block and operation.
-   *
-   * @param \Drupal\Core\Block\BlockPluginInterface $block
-   *   The block plugin.
-   *
-   * @return \Drupal\Core\Plugin\PluginFormInterface
-   *   The plugin form for the block.
-   */
-  protected function getPluginForm(BlockPluginInterface $block) {
-    return $this->pluginFormFactory->createInstance($block, 'configure');
-  }
-
 }
diff --git a/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestMultipleFormsBlock.php b/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestMultipleFormsBlock.php
deleted file mode 100644
index 64b70b22c04..00000000000
--- a/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestMultipleFormsBlock.php
+++ /dev/null
@@ -1,27 +0,0 @@
-<?php
-
-namespace Drupal\block_test\Plugin\Block;
-
-use Drupal\Core\Block\BlockBase;
-
-/**
- * Provides a block with multiple forms.
- *
- * @Block(
- *   id = "test_multiple_forms_block",
- *   forms = {
- *     "secondary" = "\Drupal\block_test\PluginForm\EmptyBlockForm"
- *   },
- *   admin_label = @Translation("Multiple forms test block")
- * )
- */
-class TestMultipleFormsBlock extends BlockBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public function build() {
-    return [];
-  }
-
-}
diff --git a/core/modules/block/tests/modules/block_test/src/PluginForm/EmptyBlockForm.php b/core/modules/block/tests/modules/block_test/src/PluginForm/EmptyBlockForm.php
deleted file mode 100644
index 6a654cbdef1..00000000000
--- a/core/modules/block/tests/modules/block_test/src/PluginForm/EmptyBlockForm.php
+++ /dev/null
@@ -1,27 +0,0 @@
-<?php
-
-namespace Drupal\block_test\PluginForm;
-
-use Drupal\Core\Form\FormStateInterface;
-use Drupal\Core\Plugin\PluginFormBase;
-
-/**
- * Provides a form for a block that is empty.
- */
-class EmptyBlockForm extends PluginFormBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
-    return $form;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
-    // Intentionally empty.
-  }
-
-}
diff --git a/core/modules/block/tests/src/Unit/BlockFormTest.php b/core/modules/block/tests/src/Unit/BlockFormTest.php
index d8efe2b7910..09f450b853a 100644
--- a/core/modules/block/tests/src/Unit/BlockFormTest.php
+++ b/core/modules/block/tests/src/Unit/BlockFormTest.php
@@ -3,7 +3,6 @@
 namespace Drupal\Tests\block\Unit;
 
 use Drupal\block\BlockForm;
-use Drupal\Core\Plugin\PluginFormFactoryInterface;
 use Drupal\Tests\UnitTestCase;
 
 /**
@@ -55,13 +54,6 @@ class BlockFormTest extends UnitTestCase {
    */
   protected $contextRepository;
 
-  /**
-   * The plugin form manager.
-   *
-   * @var \Drupal\Core\Plugin\PluginFormFactoryInterface|\Prophecy\Prophecy\ProphecyInterface
-   */
-  protected $pluginFormFactory;
-
   /**
    * {@inheritdoc}
    */
@@ -79,7 +71,6 @@ class BlockFormTest extends UnitTestCase {
       ->method('getStorage')
       ->will($this->returnValue($this->storage));
 
-    $this->pluginFormFactory = $this->prophesize(PluginFormFactoryInterface::class);
   }
 
   /**
@@ -108,7 +99,7 @@ class BlockFormTest extends UnitTestCase {
       ->method('getQuery')
       ->will($this->returnValue($query));
 
-    $block_form_controller = new BlockForm($this->entityManager, $this->conditionManager, $this->contextRepository, $this->language, $this->themeHandler, $this->pluginFormFactory->reveal());
+    $block_form_controller = new BlockForm($this->entityManager, $this->conditionManager, $this->contextRepository, $this->language, $this->themeHandler);
 
     // Ensure that the block with just one other instance gets the next available
     // name suggestion.
diff --git a/core/tests/Drupal/KernelTests/Core/Block/MultipleBlockFormTest.php b/core/tests/Drupal/KernelTests/Core/Block/MultipleBlockFormTest.php
deleted file mode 100644
index 2fbe025acfe..00000000000
--- a/core/tests/Drupal/KernelTests/Core/Block/MultipleBlockFormTest.php
+++ /dev/null
@@ -1,38 +0,0 @@
-<?php
-
-namespace Drupal\KernelTests\Core\Block;
-
-use Drupal\block_test\PluginForm\EmptyBlockForm;
-use Drupal\KernelTests\KernelTestBase;
-
-/**
- * Tests that blocks can have multiple forms.
- *
- * @group block
- */
-class MultipleBlockFormTest extends KernelTestBase {
-
-  /**
-   * {@inheritdoc}
-   */
-  public static $modules = ['system', 'block', 'block_test'];
-
-  /**
-   * Tests that blocks can have multiple forms.
-   */
-  public function testMultipleForms() {
-    $configuration = ['label' => 'A very cool block'];
-    $block = \Drupal::service('plugin.manager.block')->createInstance('test_multiple_forms_block', $configuration);
-
-    $form_object1 = \Drupal::service('plugin_form.factory')->createInstance($block, 'configure');
-    $form_object2 = \Drupal::service('plugin_form.factory')->createInstance($block, 'secondary');
-
-    // Assert that the block itself is used for the default form.
-    $this->assertSame($block, $form_object1);
-
-    // Ensure that EmptyBlockForm is used and the plugin is set.
-    $this->assertInstanceOf(EmptyBlockForm::class, $form_object2);
-    $this->assertAttributeEquals($block, 'plugin', $form_object2);
-  }
-
-}
diff --git a/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php b/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php
index feac00467c2..8cc0f81c1aa 100644
--- a/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Plugin/DefaultPluginManagerTest.php
@@ -3,8 +3,6 @@
 namespace Drupal\Tests\Core\Plugin;
 
 use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Form\FormStateInterface;
-use Drupal\Core\Plugin\PluginFormInterface;
 use Drupal\Tests\UnitTestCase;
 
 /**
@@ -340,98 +338,4 @@ class DefaultPluginManagerTest extends UnitTestCase {
     $this->assertInternalType('int', $cache_max_age);
   }
 
-  /**
-   * @covers ::processDefinition
-   * @dataProvider providerTestProcessDefinition
-   */
-  public function testProcessDefinition($definition, $expected) {
-    $module_handler = $this->prophesize(ModuleHandlerInterface::class);
-    $plugin_manager = new TestPluginManagerWithDefaults($this->namespaces, $this->expectedDefinitions, $module_handler->reveal(), NULL);
-
-    $plugin_manager->processDefinition($definition, 'the_plugin_id');
-    $this->assertEquals($expected, $definition);
-  }
-
-  public function providerTestProcessDefinition() {
-    $data = [];
-
-    $data['merge'][] = [
-      'foo' => [
-        'bar' => [
-          'asdf',
-        ],
-      ],
-    ];
-    $data['merge'][] = [
-      'foo' => [
-        'bar' => [
-          'baz',
-          'asdf',
-        ],
-      ],
-    ];
-
-    $object_definition = (object) [
-      'foo' => [
-        'bar' => [
-          'asdf',
-        ],
-      ],
-    ];
-    $data['object_definition'] = [$object_definition, clone $object_definition];
-
-    $data['no_form'][] = ['class' => TestPluginForm::class];
-    $data['no_form'][] = [
-      'class' => TestPluginForm::class,
-      'forms' => ['configure' => TestPluginForm::class],
-      'foo' => ['bar' => ['baz']],
-    ];
-
-    $data['default_form'][] = ['class' => TestPluginForm::class, 'forms' => ['configure' => 'stdClass']];
-    $data['default_form'][] = [
-      'class' => TestPluginForm::class,
-      'forms' => ['configure' => 'stdClass'],
-      'foo' => ['bar' => ['baz']],
-    ];
-    return $data;
-  }
-
-}
-
-class TestPluginManagerWithDefaults extends TestPluginManager {
-
-  /**
-   * {@inheritdoc}
-   */
-  protected $defaults = [
-    'foo' => [
-      'bar' => [
-        'baz',
-      ],
-    ],
-  ];
-
-}
-
-class TestPluginForm implements PluginFormInterface {
-
-  /**
-   * {@inheritdoc}
-   */
-  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
-    return [];
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
-  }
-
 }
diff --git a/core/tests/Drupal/Tests/Core/Plugin/PluginFormFactoryTest.php b/core/tests/Drupal/Tests/Core/Plugin/PluginFormFactoryTest.php
deleted file mode 100644
index fc4b77aebe1..00000000000
--- a/core/tests/Drupal/Tests/Core/Plugin/PluginFormFactoryTest.php
+++ /dev/null
@@ -1,156 +0,0 @@
-<?php
-
-namespace Drupal\Tests\Core\Plugin;
-
-use Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException;
-use Drupal\Component\Plugin\PluginAwareInterface;
-use Drupal\Core\DependencyInjection\ClassResolverInterface;
-use Drupal\Core\Plugin\PluginFormInterface;
-use Drupal\Core\Plugin\PluginFormFactory;
-use Drupal\Core\Plugin\PluginWithFormsInterface;
-use Drupal\Tests\UnitTestCase;
-use Prophecy\Argument;
-
-/**
- * @coversDefaultClass \Drupal\Core\Plugin\PluginFormFactory
- * @group Plugin
- */
-class PluginFormFactoryTest extends UnitTestCase {
-
-  /**
-   * The class resolver.
-   *
-   * @var \Drupal\Core\DependencyInjection\ClassResolverInterface|\Prophecy\Prophecy\ProphecyInterface
-   */
-  protected $classResolver;
-
-  /**
-   * The manager being tested.
-   *
-   * @var \Drupal\Core\Plugin\PluginFormFactory
-   */
-  protected $manager;
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-
-    $this->classResolver = $this->prophesize(ClassResolverInterface::class);
-    $this->manager = new PluginFormFactory($this->classResolver->reveal());
-  }
-
-  /**
-   * @covers ::createInstance
-   */
-  public function testCreateInstance() {
-    $plugin_form = $this->prophesize(PluginFormInterface::class);
-    $expected = $plugin_form->reveal();
-
-    $this->classResolver->getInstanceFromDefinition(get_class($expected))->willReturn($expected);
-
-    $plugin = $this->prophesize(PluginWithFormsInterface::class);
-    $plugin->hasFormClass('standard_class')->willReturn(TRUE);
-    $plugin->getFormClass('standard_class')->willReturn(get_class($expected));
-
-    $form_object = $this->manager->createInstance($plugin->reveal(), 'standard_class');
-    $this->assertSame($expected, $form_object);
-  }
-
-  /**
-   * @covers ::createInstance
-   */
-  public function testCreateInstanceUsingPlugin() {
-    $this->classResolver->getInstanceFromDefinition(Argument::cetera())->shouldNotBeCalled();
-
-    $plugin = $this->prophesize(PluginWithFormsInterface::class)->willImplement(PluginFormInterface::class);
-    $plugin->hasFormClass('configure')->willReturn(TRUE);
-    $plugin->getFormClass('configure')->willReturn(get_class($plugin->reveal()));
-
-    $form_object = $this->manager->createInstance($plugin->reveal(), 'configure');
-    $this->assertSame($plugin->reveal(), $form_object);
-  }
-
-  /**
-   * @covers ::createInstance
-   */
-  public function testCreateInstanceUsingPluginWithSlashes() {
-    $this->classResolver->getInstanceFromDefinition(Argument::cetera())->shouldNotBeCalled();
-
-    $plugin = $this->prophesize(PluginWithFormsInterface::class)->willImplement(PluginFormInterface::class);
-    $plugin->hasFormClass('configure')->willReturn(TRUE);
-    $plugin->getFormClass('configure')->willReturn('\\' . get_class($plugin->reveal()));
-
-    $form_object = $this->manager->createInstance($plugin->reveal(), 'configure');
-    $this->assertSame($plugin->reveal(), $form_object);
-  }
-
-  /**
-   * @covers ::createInstance
-   */
-  public function testCreateInstanceDefaultFallback() {
-    $this->classResolver->getInstanceFromDefinition(Argument::cetera())->shouldNotBeCalled();
-
-    $plugin = $this->prophesize(PluginWithFormsInterface::class)->willImplement(PluginFormInterface::class);
-    $plugin->hasFormClass('missing')->willReturn(FALSE);
-    $plugin->hasFormClass('fallback')->willReturn(TRUE);
-    $plugin->getFormClass('fallback')->willReturn(get_class($plugin->reveal()));
-
-    $form_object = $this->manager->createInstance($plugin->reveal(), 'missing', 'fallback');
-    $this->assertSame($plugin->reveal(), $form_object);
-  }
-
-  /**
-   * @covers ::createInstance
-   */
-  public function testCreateInstancePluginAware() {
-    $plugin_form = $this->prophesize(PluginFormInterface::class)->willImplement(PluginAwareInterface::class);
-
-    $expected = $plugin_form->reveal();
-
-    $this->classResolver->getInstanceFromDefinition(get_class($expected))->willReturn($expected);
-
-    $plugin = $this->prophesize(PluginWithFormsInterface::class);
-    $plugin->hasFormClass('operation_aware')->willReturn(TRUE);
-    $plugin->getFormClass('operation_aware')->willReturn(get_class($expected));
-
-    $plugin_form->setPlugin($plugin->reveal())->shouldBeCalled();
-
-    $form_object = $this->manager->createInstance($plugin->reveal(), 'operation_aware');
-    $this->assertSame($expected, $form_object);
-  }
-
-  /**
-   * @covers ::createInstance
-   */
-  public function testCreateInstanceDefinitionException() {
-    $this->setExpectedException(InvalidPluginDefinitionException::class, 'The "the_plugin_id" plugin did not specify a "anything" form class');
-
-    $plugin = $this->prophesize(PluginWithFormsInterface::class);
-    $plugin->getPluginId()->willReturn('the_plugin_id');
-    $plugin->hasFormClass('anything')->willReturn(FALSE);
-
-    $form_object = $this->manager->createInstance($plugin->reveal(), 'anything');
-    $this->assertSame(NULL, $form_object);
-  }
-
-  /**
-   * @covers ::createInstance
-   */
-  public function testCreateInstanceInvalidException() {
-    $this->setExpectedException(InvalidPluginDefinitionException::class, 'The "the_plugin_id" plugin did not specify a valid "invalid" form class, must implement \Drupal\Core\Plugin\PluginFormInterface');
-
-    $expected = new \stdClass();
-    $this->classResolver->getInstanceFromDefinition(get_class($expected))->willReturn($expected);
-
-    $plugin = $this->prophesize(PluginWithFormsInterface::class);
-    $plugin->getPluginId()->willReturn('the_plugin_id');
-    $plugin->hasFormClass('invalid')->willReturn(TRUE);
-    $plugin->getFormClass('invalid')->willReturn(get_class($expected));
-
-    $form_object = $this->manager->createInstance($plugin->reveal(), 'invalid');
-    $this->assertSame(NULL, $form_object);
-  }
-
-}