diff --git a/core/modules/file/src/Tests/FileValidationConstraintTest.php b/core/modules/file/src/Tests/FileValidationConstraintTest.php
new file mode 100644
index 0000000..88e4fbe
--- /dev/null
+++ b/core/modules/file/src/Tests/FileValidationConstraintTest.php
@@ -0,0 +1,132 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\file\Tests\FileValidationConstraintTest.
+ */
+
+namespace Drupal\file\Tests;
+
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+
+/**
+ * Tests the file validation constraint.
+ *
+ * @group file
+ */
+class FileValidationConstraintTest extends FileManagedUnitTestBase {
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  public static $modules = array('entity_test', 'field');
+
+  /**
+   * Tests basic file field validations when attaching to entities.
+   */
+  public function testFileValidation() {
+    // Create a file which should be secret.
+
+    // Create a text and a PDF field.
+    $this->createFileField('field_text_file', 'entity_test', 'entity_test', [], ['file_extensions' => 'txt']);
+    $this->createFileField('field_pdf_file', 'entity_test', 'entity_test', [], ['file_extensions' => 'pdf']);
+
+    // Create a text file try to use it in both fields.
+    $file = $this->createFile('test.txt');
+
+    $entity_test = EntityTest::create([
+      'name' => 'Test',
+      'uid' => 1,
+      'field_text_file' => [
+        0 => [
+          'target_id' => $file->id(),
+        ],
+      ],
+      'field_pdf_file' => [
+        0 => [
+          'target_id' => $file->id(),
+        ],
+      ],
+    ]);
+    $violations = $entity_test->validate();
+    $this->assertEqual(1, count($violations));
+    $this->assertEqual($violations[0]->getPropertyPath(), "field_pdf_file.0");
+    $this->assertEqual($violations[0]->getMessage(), t('Only files with the following extensions are allowed: %files-allowed.', ['%files-allowed' => 'pdf']));
+  }
+
+  /**
+   * Creates a new file field.
+   *
+   * @param string $name
+   *   The name of the new field (all lowercase), exclude the "field_" prefix.
+   * @param string $entity_type
+   *   The entity type.
+   * @param string $bundle
+   *   The bundle that this field will be added to.
+   * @param array $storage_settings
+   *   A list of field storage settings that will be added to the defaults.
+   * @param array $field_settings
+   *   A list of instance settings that will be added to the instance defaults.
+   * @param array $widget_settings
+   *   A list of widget settings that will be added to the widget defaults.
+   *
+   * @return \Drupal\Core\Entity\EntityInterface
+   */
+  protected function createFileField($name, $entity_type, $bundle, $storage_settings = [], $field_settings = [], $widget_settings = []) {
+    $field_storage = FieldStorageConfig::create([
+      'entity_type' => $entity_type,
+      'field_name' => $name,
+      'type' => 'file',
+      'settings' => $storage_settings,
+      'cardinality' => !empty($storage_settings['cardinality']) ? $storage_settings['cardinality'] : 1,
+    ]);
+    $field_storage->save();
+
+    $this->attachFileField($name, $entity_type, $bundle, $field_settings, $widget_settings);
+    return $field_storage;
+  }
+
+  /**
+   * Attaches a file field to an entity.
+   *
+   * @param string $name
+   *   The name of the new field (all lowercase), exclude the "field_" prefix.
+   * @param string $entity_type
+   *   The entity type this field will be added to.
+   * @param string $bundle
+   *   The bundle this field will be added to.
+   * @param array $field_settings
+   *   A list of field settings that will be added to the defaults.
+   * @param array $widget_settings
+   *   A list of widget settings that will be added to the widget defaults.
+   */
+  protected function attachFileField($name, $entity_type, $bundle, $field_settings = [], $widget_settings = []) {
+    FieldConfig::create([
+      'field_name' => $name,
+      'label' => $name,
+      'entity_type' => $entity_type,
+      'bundle' => $bundle,
+      'required' => !empty($field_settings['required']),
+      'settings' => $field_settings,
+    ])->save();
+
+    entity_get_form_display($entity_type, $bundle, 'default')
+      ->setComponent($name, [
+        'type' => 'file_generic',
+        'settings' => $widget_settings,
+      ])
+      ->save();
+    // Assign display settings.
+    entity_get_display($entity_type, $bundle, 'default')
+      ->setComponent($name, [
+        'label' => 'hidden',
+        'type' => 'file_default',
+      ])
+      ->save();
+  }
+
+}