Add feedback integration test

tests/FeedbackSubmittedTest.php

+<?php namespace Tests;
+
+class FeedbackSubmitted extends AttemptTestCase {
+    protected function constructInput() {
+        return array_merge(parent::constructInput(), [
+            'eventname' => '\mod_feedback\event\response_submitted',
+            'objecttable' => 'feedback_completed',
+            'objectid' => 1,
+        ]);
+    }
+}