ENH Add extension required for new elemental behat test

code/elemental/FileElementalExtension.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace SilverStripe\FrameworkTest\Elemental\Extension;
+
+use SilverStripe\Assets\File;
+use SilverStripe\Core\Extension;
+use SilverStripe\Forms\FieldList;
+
+class FileElementalExtension extends Extension
+{
+    private static $has_one = [
+        'MyFile' => File::class,
+    ];
+
+    private static $owns = [
+        'MyFile',
+    ];
+
+    public function updateCMSFields(FieldList $fields)
+    {
+        $fields->removeByName('HTML');
+    }
+}