1.Zf2Service.php

<?php

namespace Foo;

use Zend\Http\Client   as HttpClient;
use Zend\Http\Response as HttpResponse;
use Zend\Http\Exception\ExceptionInterface as HttpException;

use Zend\Json\Json;

class Service
{
    const API_HOST = 'http://api.postcodeapi.nu/';
    
    protected $client;
    
    public function setClient(HttpClient $client)
    {
        $this->client = $client;
    }
    
    public function getClient()
    {
        if (null === $this->client) {
            $this->client = new HttpClient;
        }
        
        return $this->client;
    }
    
    public function do()
    {
        // $params or something
        
        $uri      = self::API_HOST . implode('/', $params);
        $client   = $this->getClient();
        
        try {
            $response = $client->send($uri);   
        } catch (HttpException $e) {
            return $this->handleError(500, $e->getMessage());
        }
        
        return $this->handleResponse($response);
    }
    
    public function handleResponse(HttpResponse $response)
    {
        $body = $response->getBody();
        if (!$response->isSuccess()) {
            $code = $response->getStatusCode();
            return $this->handleError($code, $body);
        }
        
        $data = Json::decode($body);
        switch ($data->success) {
            // etc
        }
    }
}

2.Zf2ServiceTest.php

<?php

namespace FooTest;

use Foo\Service;
use PHPUnit_Framework_TestCase as TestCase;
use Zend\Http\Response as HttpResponse;

class SerivceTest extends TestCase
{
    protected $service;
    protected $httpAdapter;
    
    public function setUp()
    {
        $this->service     = new Service;
        $this->httpAdapter = new  Zend\Http\Client\Adapter\Test;
        $this->service->getClient()->setAdapter($this->httpAdapter);
    }
    
    public function testResponseHandlesNon20xResponse()
    {
        $service = $this->service;
        $adapter = $this->httpAdapter;
        
        $response = new HttpResponse;
        $response->setStatusCode(500);
        $response->setContent('FooBarBaz');
        $adapter->setResponse($response);
        
        $result = $service->do();
        
        $this->assertInstanceOf('Foo\Service\Error', $result);
        $this->assertEquals(500, $result->getCode());
        $this->assertEquals('FooBarBaz', $result->getMessage());
    }
}

3.ServiceInterface.php

<?php

namespace MyNamespace;

use Zend\Http\Client as HttpClient;

class MyService
{
    protected $apiKey;
    protected $httpClient;
    
    public function __construct($apiKey, HttpClient $httpClient = null)
    {
        $this->apiKey = $apiKey;
        
        if (null !== $httpClient) {
            $this->httpClient = $httpClient;
        }
    }
    
    public function find($postcode, $houseNumber=null)
    {
        / direct $postcode en $houseNumber gebruiken
    }
}