diff --git a/tests/modules/paragraphs_test/paragraphs_test.module b/tests/modules/paragraphs_test/paragraphs_test.module
index 7960532..9d57dfd 100644
--- a/tests/modules/paragraphs_test/paragraphs_test.module
+++ b/tests/modules/paragraphs_test/paragraphs_test.module
@@ -5,14 +5,14 @@
  * Test module for testing the paragraphs module.
  */
 
-use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
+use Drupal\Core\Render\Element;
 use Drupal\paragraphs\ParagraphInterface;
 use Drupal\paragraphs\Plugin\Field\FieldWidget\ParagraphsWidget;
 
 /**
  * Implements hook_paragraphs_widget_actions_alter().
  */
-function paragraphs_test_paragraphs_widget_actions_alter(&$widget_actions, &$context) {
+function paragraphs_test_paragraphs_widget_actions_alter(&$widget_actions) {
   if (\Drupal::state()->get('paragraphs_test_dropbutton')) {
     $widget_actions['dropdown_actions']['test_button'] = ParagraphsWidget::expandButton([
       '#type' => 'submit',
@@ -29,7 +29,7 @@ function paragraphs_test_paragraphs_widget_actions_alter(&$widget_actions, &$con
 /**
  * Implements hook_ENTITY_TYPE_view().
  */
-function paragraphs_test_paragraph_view(array &$build, ParagraphInterface $entity, EntityViewDisplayInterface $display, $view_mode) {
+function paragraphs_test_paragraph_view(array &$build, ParagraphInterface $entity) {
   if (!\Drupal::state('paragraphs_test_parent')) {
     return;
   }
@@ -38,3 +38,55 @@ function paragraphs_test_paragraph_view(array &$build, ParagraphInterface $entit
   $parent_field_name = $entity->get('parent_field_name')->value;
   drupal_set_message("Parent: $parent_type/$parent_id/$parent_field_name", 'status', TRUE);
 }
+
+/**
+ * Implements hook_form_paragraphs_subform_alter().
+ */
+function paragraphs_test_form_paragraphs_subform_alter(array &$subform) {
+  foreach (Element::children($subform) as $key) {
+    // Check if container suffix empty. Needs to avoid join warning.
+    if (empty($subform[$key]['#suffix'])) {
+      $subform[$key]['#suffix'] = '';
+    }
+    $subform[$key]['#suffix'] .= 'Here is element added by hook_form_paragraphs_subform_alter(). Key - ' . $key . '<br>';
+  }
+}
+
+/**
+ * Implements hook_form_paragraphs_subform_TYPE_alter().
+ */
+function paragraphs_test_form_paragraphs_subform_text_paragraph_alter(array &$subform) {
+  foreach (Element::children($subform) as $key) {
+    // Check if container suffix empty. Needs to avoid join warning.
+    if (empty($subform[$key]['#suffix'])) {
+      $subform[$key]['#suffix'] = '';
+    }
+    $subform[$key]['#suffix'] .= 'Here is subform for paragraph type `text_paragraph` added by hook_form_paragraphs_subform_TYPE_alter()<br>';
+  }
+}
+
+/**
+ * Implements hook_form_paragraphs_subform_WIDGET_alter().
+ */
+function paragraphs_test_form_paragraphs_subform_experimental_alter(array &$subform) {
+  foreach (Element::children($subform) as $key) {
+    // Check if container suffix empty. Needs to avoid join warning.
+    if (empty($subform[$key]['#suffix'])) {
+      $subform[$key]['#suffix'] = '';
+    }
+    $subform[$key]['#suffix'] .= 'Here is subform for experimental paragraph widget added by hook_form_paragraphs_subform_WIDGET_alter()<br>';
+  }
+}
+
+/**
+ * Implements hook_form_paragraphs_subform_WIDGET_TYPE_alter().
+ */
+function paragraphs_test_form_paragraphs_subform_experimental_text_paragraph_alter(array &$subform) {
+  foreach (Element::children($subform) as $key) {
+    // Check if container suffix empty. Needs to avoid join warning.
+    if (empty($subform[$key]['#suffix'])) {
+      $subform[$key]['#suffix'] = '';
+    }
+    $subform[$key]['#suffix'] .= 'Here is subform for experimental paragraph widget type `text_paragraph` added by hook_form_paragraphs_subform_WIDGET_TYPE_alter()<br>';
+  }
+}
diff --git a/tests/src/Functional/ParagraphsExperimentalSubformTest.php b/tests/src/Functional/ParagraphsExperimentalSubformTest.php
new file mode 100644
index 0000000..4e06a87
--- /dev/null
+++ b/tests/src/Functional/ParagraphsExperimentalSubformTest.php
@@ -0,0 +1,115 @@
+<?php
+
+namespace Drupal\Tests\paragraphs\Functional;
+
+use Drupal\paragraphs\Tests\Classic\ParagraphsCoreVersionUiTestTrait;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\paragraphs\FunctionalJavascript\LoginAdminTrait;
+use Drupal\Tests\paragraphs\FunctionalJavascript\ParagraphsTestBaseTrait;
+
+/**
+ * Tests paragraphs subforms hooks.
+ *
+ * @group paragraphs
+ */
+class ParagraphsExperimentalSubformTest extends BrowserTestBase {
+
+  use LoginAdminTrait;
+  use ParagraphsCoreVersionUiTestTrait;
+  use ParagraphsTestBaseTrait;
+
+  /**
+   * Modules to enable.
+   *
+   * @var string[]
+   */
+  public static $modules = [
+    'paragraphs_test',
+    'node',
+    'paragraphs',
+    'field',
+    'field_ui',
+  ];
+
+  /**
+   * Tests the hooks for paragraph subforms.
+   */
+  public function testParagraphsWidgetSubformAlter() {
+    $this->addParagraphedContentType('paragraphed_test');
+
+    $permissions = [
+      'administer content types',
+      'administer node fields',
+      'administer paragraphs types',
+      'administer node form display',
+      'administer paragraph fields',
+      'administer paragraph form display',
+      'create paragraphed_test content',
+      'edit any paragraphed_test content',
+    ];
+    $this->loginAsAdmin($permissions, TRUE);
+
+    // Add new Paragraph types.
+    $this->addParagraphsType('text_paragraph');
+    $this->addFieldtoParagraphType('text_paragraph', 'field_text', 'text_long');
+
+    $this->addParagraphsType('another_paragraph');
+    $this->addFieldtoParagraphType('another_paragraph', 'field_title', 'string');
+
+    // Test for the node add form.
+    // New paragraphs.
+    $this->drupalGet('node/add/paragraphed_test');
+    $this->getSession()->getPage()->findButton('field_paragraphs_text_paragraph_add_more')->press();
+    $this->getSession()->getPage()->findButton('field_paragraphs_another_paragraph_add_more')->press();
+
+    // Checks that text added by hook_form_paragraphs_subform_alter() exists.
+    $this->assertSession()->pageTextContains('Here is element added by hook_form_paragraphs_subform_alter(). Key - field_text');
+    $this->assertSession()->pageTextContains('Here is element added by hook_form_paragraphs_subform_alter(). Key - field_title');
+
+    // Checks text added by hook_form_paragraphs_subform_TYPE_alter() exists.
+    $this->assertSession()->pageTextContains('Here is subform for paragraph type `text_paragraph` added by hook_form_paragraphs_subform_TYPE_alter()');
+
+    // Checks text added by hook_form_paragraphs_subform_WIDGET_alter() exists.
+    $this->assertSession()->pageTextContains('Here is subform for experimental paragraph widget added by hook_form_paragraphs_subform_WIDGET_alter()');
+
+    // Checks text added by
+    // hook_form_paragraphs_subform_WIDGET_TYPE_alter() exists.
+    $this->assertSession()->pageTextContains('Here is subform for experimental paragraph widget type `text_paragraph` added by hook_form_paragraphs_subform_WIDGET_TYPE_alter()');
+
+    // Check for node editing with closed paragraphs.
+    $edit = [
+      'title[0][value]' => 'Paragraphs Subform test node',
+      'field_paragraphs[0][subform][field_text][0][value]' => 'Text paragraph',
+      'field_paragraphs[1][subform][field_title][0][value]' => 'Title paragraph',
+    ];
+    $this->drupalPostForm(NULL, $edit, t('Save'));
+    $node = $this->drupalGetNodeByTitle('Paragraphs Subform test node');
+
+    // Set the settings to "Closed" to check that subforms are clean.
+    $settings = [
+      'edit_mode' => 'closed',
+      'closed_mode' => 'summary',
+      'autocollapse' => 'none',
+    ];
+    $this->setParagraphsWidgetSettings('paragraphed_test', 'field_paragraphs', $settings);
+
+    $this->drupalGet('node/' . $node->id() . '/edit');
+
+    // Check if all subforms are closed.
+    $this->assertSession()->pageTextNotContains('Here is element added by');
+    $this->assertSession()->pageTextNotContains('Here is subform for experimental paragraph widget');
+
+    // Open first `text_paragraph`.
+    $this->getSession()->getPage()->findButton('field_paragraphs_0_edit')->press();
+
+    // It should contains all texts except 'Here is element added by
+    // hook_form_paragraphs_subform_alter(). Key - field_title'.
+    $this->assertSession()->pageTextContains('Here is element added by hook_form_paragraphs_subform_alter(). Key - field_text');
+    $this->assertSession()->pageTextContains('Here is subform for paragraph type `text_paragraph` added by hook_form_paragraphs_subform_TYPE_alter()');
+    $this->assertSession()->pageTextContains('Here is subform for experimental paragraph widget added by hook_form_paragraphs_subform_WIDGET_alter()');
+    $this->assertSession()->pageTextContains('Here is subform for experimental paragraph widget type `text_paragraph` added by hook_form_paragraphs_subform_WIDGET_TYPE_alter()');
+    $this->assertSession()->pageTextNotContains('Here is element added by hook_form_paragraphs_subform_alter(). Key - field_title');
+
+  }
+
+}