diff --git a/core/modules/file/src/Tests/FileFieldWidgetTest.php b/core/modules/file/src/Tests/FileFieldWidgetTest.php
index 414c86b..0276c81 100644
--- a/core/modules/file/src/Tests/FileFieldWidgetTest.php
+++ b/core/modules/file/src/Tests/FileFieldWidgetTest.php
@@ -428,6 +428,9 @@ function testWidgetValidation() {
       $test_file_image = $this->getTestFile('image');
       $name = 'files[' . $field_name . '_0]';
 
+      // Check field is marked with expected attr for client-side validation.
+      $this->assertFieldByXPath('//input[@type="file" and @data-drupal-validate-extensions="txt"]', null, 'data-drupal-validate-extensions is present');
+
       // Upload file with incorrect extension, check for validation error.
       $edit[$name] = drupal_realpath($test_file_image->getFileUri());
       switch ($type) {
diff --git a/core/modules/file/src/Tests/FileManagedFileElementTest.php b/core/modules/file/src/Tests/FileManagedFileElementTest.php
index 07102a0..e9aa2a2 100644
--- a/core/modules/file/src/Tests/FileManagedFileElementTest.php
+++ b/core/modules/file/src/Tests/FileManagedFileElementTest.php
@@ -18,6 +18,10 @@ function testManagedFile() {
     $this->drupalGet('file/test');
     $this->assertFieldByXpath('//input[@name="files[nested_file]" and @size="13"]', NULL, 'The custom #size attribute is passed to the child upload element.');
 
+    // Check that relevant data- attributes are present for validations
+    $this->drupalGet('file/test/validation/extension');
+    $this->assertFieldByXPath('//input[@name="files[file]" and @data-drupal-validate-extensions="txt"]', NULL, 'The data-drupal-validate-extensions attribute is present on the upload element.');
+
     // Perform the tests with all permutations of $form['#tree'],
     // $element['#extended'], and $element['#multiple'].
     $test_file = $this->getTestFile('text');
diff --git a/core/modules/file/tests/file_module_test/file_module_test.routing.yml b/core/modules/file/tests/file_module_test/file_module_test.routing.yml
index 15f7d0f..0c85f6e 100644
--- a/core/modules/file/tests/file_module_test/file_module_test.routing.yml
+++ b/core/modules/file/tests/file_module_test/file_module_test.routing.yml
@@ -8,3 +8,11 @@ file_module_test.managed_test:
     default_fids: NULL
   requirements:
     _access: 'TRUE'
+
+file_module_test.managed_validations_test:
+  path: '/file/test/validation/{validation_type}'
+  defaults:
+    _form: '\Drupal\file_module_test\Form\FileModuleTestValidationForm'
+    validation_type: 'extension'
+  requirements:
+    _access: 'TRUE'
diff --git a/core/modules/file/tests/file_module_test/src/Form/FileModuleTestValidationForm.php b/core/modules/file/tests/file_module_test/src/Form/FileModuleTestValidationForm.php
index e69de29..9674b09 100644
--- a/core/modules/file/tests/file_module_test/src/Form/FileModuleTestValidationForm.php
+++ b/core/modules/file/tests/file_module_test/src/Form/FileModuleTestValidationForm.php
@@ -0,0 +1,70 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\file_module_test\Form\FileModuleTestForm.
+ */
+
+namespace Drupal\file_module_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Form controller for file_module_test module.
+ */
+class FileModuleTestValidationForm extends FormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'file_module_test_validation_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   *
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   * @param string $validation_type
+   *   The validation being tested, ie 'extension', 'size'
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, $validation_type = 'extension') {
+    switch ($validation_type) {
+      case 'extension':
+        $validator = ['file_validate_extensions' => ['txt']];
+        break;
+      case 'size':
+        $validator = ['file_validate_size' => [1024]];
+        break;
+      default:
+        return FALSE;
+    }
+
+    $form['file'] = array(
+      '#type' => 'managed_file',
+      '#title' => $this->t('Managed File'),
+      '#upload_location' => 'public://test',
+      '#progress_message' => $this->t('Please wait...'),
+      '#upload_validators' => $validator,
+    );
+
+    $form['submit'] = array(
+      '#type' => 'submit',
+      '#value' => $this->t('Save'),
+    );
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    drupal_set_message($this->t('Test submission handler was allowed to execute.'));
+  }
+
+}
diff --git a/core/modules/image/src/Tests/ImageFieldDisplayTest.php b/core/modules/image/src/Tests/ImageFieldDisplayTest.php
index 666a791..61a6c9d 100644
--- a/core/modules/image/src/Tests/ImageFieldDisplayTest.php
+++ b/core/modules/image/src/Tests/ImageFieldDisplayTest.php
@@ -312,8 +312,13 @@ function testImageFieldSettings() {
       'files[' . $field_name . '_2][]' => drupal_realpath($test_image->uri),
     );
     $this->drupalPostAjaxForm(NULL, $edit, $field_name . '_2_upload_button');
-    $this->assertNoRaw('<input multiple type="file" id="edit-' . strtr($field_name, '_', '-') . '-2-upload" name="files[' . $field_name . '_2][]" size="22" class="js-form-file form-file">');
-    $this->assertRaw('<input multiple type="file" id="edit-' . strtr($field_name, '_', '-') . '-3-upload" name="files[' . $field_name . '_3][]" size="22" class="js-form-file form-file">');
+    $this->assertNoFieldByXPath('//input[@id="edit-' . strtr($field_name, '_', '-') . '-2-upload"]', 'Upload field for second file not present after it is uploaded.');
+
+    $this->assertTrue($this->cssSelect('input#edit-' . strtr($field_name, '_', '-') . '-3-upload[multiple=multiple]'), 'Third file field presented having multiple attribute');
+    $this->assertFieldByName('files[' . $field_name . '_3][]', null, 'Third file field has correct name');
+    $this->assertTrue($this->cssSelect('input[id=edit-' . strtr($field_name, '_', '-') . '-3-upload][size=22]'), 'Third file field presented having correct size attribute');
+    $this->assertTrue($this->cssSelect('input.js-form-file.form-file[id=edit-' . strtr($field_name, '_', '-') . '-3-upload]'), 'Third file field presented having correct css classes');
+    $this->assertTrue($this->cssSelect('input[id=edit-' . strtr($field_name, '_', '-') . "-3-upload][data-drupal-validate-extensions=$test_image_extension]"), 'Third file field presented having correct data-drupal-validate-extensions');
   }
 
   /**