Added a Docker-based fresh WordPress integration test

src/helpers.php

@@ -1,10 +1,13 @@
 <?php
 
 if (!function_exists('view')) {
-    function view(string $view)
+    function view(string $view): string
     {
         $basedir = plugin_dir_path(__FILE__);
+        ob_start();
         include "{$basedir}resources/views/$view.php";
+
+        return ob_get_clean();
     }
 }