<?php

namespace Delighted;

class Metrics extends Resource
{
    public static function retrieve($params = [], Client $client = null)
    {
        if (is_null($client)) {
            $client = Client::getInstance();
        }

        $response = $client->get('metrics', $params);

        return new Metrics($response);
    }
}

<?php

namespace Delighted;

class Metrics extends Resource
{
    public static function retrieve($params = [])
    {
        $response = Client::get('metrics', $params);

        return new Metrics($response);
    }
}

--- 
+++ 
@@ -4,9 +4,13 @@
 
 class Metrics extends Resource
 {
-    public static function retrieve($params = [])
+    public static function retrieve($params = [], Client $client = null)
     {
-        $response = Client::get('metrics', $params);
+        if (is_null($client)) {
+            $client = Client::getInstance();
+        }
+
+        $response = $client->get('metrics', $params);
 
         return new Metrics($response);
     }
Update metrics class and allow passing Client instance
