diff --git a/core/modules/system/tests/modules/tabledrag_test/js/catchErrors.js b/core/modules/system/tests/modules/tabledrag_test/js/catchErrors.js
new file mode 100644
index 0000000..aa33001
--- /dev/null
+++ b/core/modules/system/tests/modules/tabledrag_test/js/catchErrors.js
@@ -0,0 +1,22 @@
+(function () {
+  'use strict';
+
+  window.errors = [];
+
+  function catchError(error) {
+    if (typeof(error) !== 'object') {
+      return;
+    }
+
+    window.errors.push(error);
+  }
+
+  window.onerror = function (message, url, line, column) {
+    catchError({
+      url: url,
+      line: line,
+      column: column,
+      message: message
+    });
+  };
+})();
diff --git a/core/modules/system/tests/modules/tabledrag_test/src/Form/TableDragTestForm.php b/core/modules/system/tests/modules/tabledrag_test/src/Form/TableDragTestForm.php
new file mode 100644
index 0000000..2d75d07
--- /dev/null
+++ b/core/modules/system/tests/modules/tabledrag_test/src/Form/TableDragTestForm.php
@@ -0,0 +1,100 @@
+<?php
+
+namespace Drupal\tabledrag_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Example form with several "tabledrag" tables.
+ */
+class TableDragTestForm extends FormBase {
+
+  const GROUP = 'tabledrag-test';
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'tabledrag_test_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, $type = NULL) {
+    $add_colspan = 'with-colspan' === $type;
+
+    for ($tab = 1; $tab <= 3; $tab++) {
+      $form[$tab] = [
+        '#type' => 'fieldset',
+        '#title' => $this->t('Content of "@tab" item', ['@tab' => $tab]),
+      ];
+
+      $form[$tab]['table'] = [
+        '#type' => 'table',
+        '#sticky' => FALSE,
+        '#header' => [
+          $this->t('Column 1'),
+          $this->t('Column 2'),
+          $this->t('Weight'),
+        ],
+        '#attributes' => [
+          'id' => "table_tab$tab",
+        ],
+      ];
+
+      for ($i = 0; $i < 3; $i++) {
+        $row = [];
+
+        $row['column1'] = [
+          '#type' => 'textfield',
+        ];
+
+        $row['column2'] = [
+          '#type' => 'textfield',
+        ];
+
+        $row['weight'] = [
+          '#type' => 'weight',
+          '#attributes' => ['class' => [static::GROUP]],
+        ];
+
+        $form[$tab]['table'][] = $row;
+      }
+
+      $form[$tab]['table']['custom-row'] = [];
+
+      $form[$tab]['table']['custom-row']['button'] = [
+        '#type' => 'button',
+        '#value' => t('Add new item'),
+      ];
+
+      if ($add_colspan) {
+        $form[$tab]['table']['custom-row']['button']['#wrapper_attributes'] = [
+          'colspan' => count($form[$tab]['table']['#header']),
+        ];
+      }
+
+      drupal_attach_tabledrag($form[$tab]['table'], [
+        'group' => static::GROUP,
+        'action' => 'order',
+        'table_id' => $form[$tab]['table']['#attributes']['id'],
+        'relationship' => 'sibling',
+      ]);
+    }
+
+    // Add the library for collecting JS errors in "window.errors" variable.
+    $form['#attached']['library'][] = 'tabledrag_test/base';
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+
+  }
+
+}
diff --git a/core/modules/system/tests/modules/tabledrag_test/tabledrag_test.info.yml b/core/modules/system/tests/modules/tabledrag_test/tabledrag_test.info.yml
new file mode 100644
index 0000000..e975206
--- /dev/null
+++ b/core/modules/system/tests/modules/tabledrag_test/tabledrag_test.info.yml
@@ -0,0 +1,5 @@
+name: TableDrag test
+description: Testing tabledrag
+package: Testing
+type: module
+core: 8.x
diff --git a/core/modules/system/tests/modules/tabledrag_test/tabledrag_test.libraries.yml b/core/modules/system/tests/modules/tabledrag_test/tabledrag_test.libraries.yml
new file mode 100644
index 0000000..f123da7
--- /dev/null
+++ b/core/modules/system/tests/modules/tabledrag_test/tabledrag_test.libraries.yml
@@ -0,0 +1,6 @@
+base:
+  js:
+    js/catchErrors.js:
+      # Set the weight more than in "JS_SETTING" constant, which is "200".
+      # This script should be as high as possible to catch all JS errors.
+      weight: -999
diff --git a/core/modules/system/tests/modules/tabledrag_test/tabledrag_test.routing.yml b/core/modules/system/tests/modules/tabledrag_test/tabledrag_test.routing.yml
new file mode 100644
index 0000000..0195201
--- /dev/null
+++ b/core/modules/system/tests/modules/tabledrag_test/tabledrag_test.routing.yml
@@ -0,0 +1,9 @@
+tabledrag_test.tabledrag_test_form:
+  path: /test/tabledrag/{type}
+  defaults:
+    _title: TableDrag test
+    _form: \Drupal\tabledrag_test\Form\TableDragTestForm
+    # "with-colspan" is also available.
+    type: without-colspan
+  requirements:
+    _access: 'TRUE'
diff --git a/core/modules/system/tests/modules/tabledrag_test/tests/src/FunctionalJavascript/TableDragTest.php b/core/modules/system/tests/modules/tabledrag_test/tests/src/FunctionalJavascript/TableDragTest.php
new file mode 100644
index 0000000..da43eb1
--- /dev/null
+++ b/core/modules/system/tests/modules/tabledrag_test/tests/src/FunctionalJavascript/TableDragTest.php
@@ -0,0 +1,54 @@
+<?php
+
+namespace Drupal\Tests\tabledrag_test\FunctionalJavascript;
+
+/**
+ * Testing of "Drupal.tableDrag" functionality.
+ *
+ * @group tabledrag
+ */
+class TableDragTest extends TableDragTestBase {
+
+  /**
+   * Check that several tables with "tabledrag" and custom row works properly.
+   *
+   * @param array $data
+   *   An associative array where key - is a type of page with "tabledrag"
+   *   table and value - an expected "colspan" for column in a custom row
+   *   of that table.
+   */
+  public function testTableDragCustomRow(array $data = ['without-colspan' => NULL, 'with-colspan' => 2]) {
+    foreach ($data as $type => $expected_colspan) {
+      $this->drupalGet("test/tabledrag/$type");
+      $this->assertEmpty($this->getJsErrors(), 'No JS errors on the page.');
+
+      for ($tab = 1; $tab <= 3; $tab++) {
+        $selector = "#table_tab$tab > tbody > tr:nth-child(4) > td";
+        $elements = $this->cssSelect($selector);
+
+        if (empty($elements)) {
+          $this->fail(sprintf('Element not found using "%s" CSS selector.', $selector));
+        }
+
+        $this->assertEquals($expected_colspan, $elements[0]->getAttribute('colspan'));
+      }
+    }
+  }
+
+  /**
+   * Check saving a state in localStorage and "colspan" calculation.
+   */
+  public function testTableDragCustomRowWithShowingWeights() {
+    // Visit the page.
+    $this->drupalGet('test/tabledrag/with-colspan');
+    // Click on "Show row weights".
+    $this->pressTableDragSwitch(t('Show row weights'));
+    // Reload the page.
+    $this->drupalGet('test/tabledrag/with-colspan');
+    // Ensure that state has been saved in localStorage.
+    $this->assertSession()->buttonExists(t('Hide row weights'));
+    // Check correctness of the "colspan" attribute.
+    $this->testTableDragCustomRow(['with-colspan' => 3]);
+  }
+
+}
diff --git a/core/modules/system/tests/modules/tabledrag_test/tests/src/FunctionalJavascript/TableDragTestBase.php b/core/modules/system/tests/modules/tabledrag_test/tests/src/FunctionalJavascript/TableDragTestBase.php
new file mode 100644
index 0000000..fc38299
--- /dev/null
+++ b/core/modules/system/tests/modules/tabledrag_test/tests/src/FunctionalJavascript/TableDragTestBase.php
@@ -0,0 +1,63 @@
+<?php
+
+namespace Drupal\Tests\tabledrag_test\FunctionalJavascript;
+
+use Drupal\FunctionalJavascriptTests\JavascriptTestBase;
+
+/**
+ * Base class for testing "Drupal.tableDrag" functionality.
+ */
+class TableDragTestBase extends JavascriptTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['tabledrag_test'];
+
+  /**
+   * Press a button by complete name.
+   *
+   * Will press the first button found with the text.
+   *
+   * If the button is discovered and pressed, the test passes. Fail otherwise.
+   *
+   * @param string|\Drupal\Component\Render\MarkupInterface $text
+   *   Text between the button tags.
+   * @param int $index
+   *   The index number for cases where multiple links have the same
+   *   text. Defaults to 0.
+   *
+   * @see clickLink()
+   */
+  protected function pressTableDragSwitch($text, $index = 0) {
+    $buttons = $this
+      ->getSession()
+      ->getDriver()
+      ->find("//button[contains(@class, 'tabledrag-toggle-weight')][text() = '$text']");
+
+    if (empty($buttons[$index])) {
+      $this->fail(sprintf('TableDrag switch #%s is not exists on the page.', $index));
+    }
+
+    $buttons[$index]->press();
+  }
+
+  /**
+   * Returns listing of JS errors on the page.
+   *
+   * @return array[]
+   *   An array of associative arrays with the following list of items:
+   *   - url
+   *   - line
+   *   - column
+   *   - message
+   */
+  protected function getJsErrors() {
+    // The "window.errors" is of array type in JS and will be converted
+    // to array in PHP as well.
+    return $this
+      ->getSession()
+      ->evaluateScript('return window.errors');
+  }
+
+}