# Testing Guzzle Clients

Guzzle provides several tools that will enable you to easily mock the HTTP layer without needing to send requests over the internet.

- Mock handler
- History middleware
- Node.js web server for integration testing

## Mock Handler

When testing HTTP clients, you often need to simulate specific scenarios like returning a successful response, returning an error, or returning specific responses in a certain order. Because unit tests need to be predictable, easy to bootstrap, and fast, hitting an actual remote API is a test smell.

Guzzle provides a mock handler that can be used to fulfill HTTP requests with queued responses, response promises, request-aware callables, or reject them with queued throwables by shifting return values off of a queue.

```php
use GuzzleHttp\Client;
use GuzzleHttp\Handler\MockHandler;
use GuzzleHttp\HandlerStack;
use GuzzleHttp\Psr7\Response;
use GuzzleHttp\Psr7\Request;
use GuzzleHttp\Exception\RequestException;

// Create a mock and queue two responses.
$mock = new MockHandler([
    new Response(200, ['X-Foo' => 'Bar'], 'Hello, World'),
    new Response(202, ['Content-Length' => '0']),
    new RequestException('Error Communicating with Server', new Request('GET', 'test'))
]);

$handlerStack = HandlerStack::create($mock);
$client = new Client(['handler' => $handlerStack]);

// The first request is intercepted with the first response.
$response = $client->request('GET', '/');
echo $response->getStatusCode();
//> 200
echo $response->getBody();
//> Hello, World
// The second request is intercepted with the second response.
echo $client->request('GET', '/')->getStatusCode();
//> 202

// Reset the queue and queue up a new response
$mock->reset();
$mock->append(new Response(201));

// As the mock was reset, the new response is the 201 CREATED,
// instead of the previously queued RequestException
echo $client->request('GET', '/')->getStatusCode();
//> 201
```

When no more responses are in the queue and a request is sent, an `OutOfBoundsException` is thrown.

Queued callables receive the `Psr\Http\Message\RequestInterface` and request options array passed to the mock handler. They may return a `Psr\Http\Message\ResponseInterface`, a `GuzzleHttp\Promise\PromiseInterface`, or a throwable rejection reason.

The optional `MockHandler` constructor callbacks are invoked with the fulfilled response or rejected reason after the queued value has settled.

## History Middleware

When using things like the `Mock` handler, you often need to know if the requests you expected to send were sent exactly as you intended. While the mock handler responds with mocked responses, the history middleware maintains a history of the requests that were sent by a client.

```php
use GuzzleHttp\Client;
use GuzzleHttp\HandlerStack;
use GuzzleHttp\Middleware;

$container = [];
$history = Middleware::history($container);

$handlerStack = HandlerStack::create();
// or $handlerStack = HandlerStack::create($mock); if using the Mock handler.

// Add the history middleware to the handler stack.
$handlerStack->push($history);

$client = new Client(['handler' => $handlerStack]);

$client->request('GET', 'http://httpbin.org/get');
$client->request('HEAD', 'http://httpbin.org/get');

// Count the number of transactions
echo count($container);
//> 2

// Iterate over the transaction history. Each transaction contains:
// - request: the request that was sent
// - response: the response, or null when the transfer was rejected
// - error: the rejection reason, or null when the transfer succeeded
// - options: the request options used for the transfer
foreach ($container as $transaction) {
    echo $transaction['request']->getMethod();
    //> GET, HEAD
    if ($transaction['response']) {
        echo $transaction['response']->getStatusCode();
        //> 200, 200
    } elseif ($transaction['error']) {
        echo $transaction['error'];
        //> exception
    }
    var_dump($transaction['options']);
    //> dumps the request options of the sent request.
}
```

## Test Web Server

Using mock responses is almost always enough when testing a web service client. When implementing custom [HTTP handlers](handlers-and-middleware.md), you'll need to send actual HTTP requests in order to sufficiently test the handler. However, a best practice is to contact a local web server rather than a server over the internet.

- Tests are more reliable
- Tests do not require a network connection
- Tests have no external dependencies

### Using the test server

> [!TIP]
> You almost never need to use this test web server. You should only ever consider using it when developing HTTP handlers. The test web server is not necessary for mocking requests. For that, please use the Mock handler and history middleware.

The test server is distributed separately from `guzzlehttp/guzzle` as the `guzzlehttp/test-server` Composer package. It is not installed with Guzzle by default. The package provides a node.js server that receives requests and returns responses from a queue. It requires Node.js `^20.19 || ^22.13 || >=24` available as `node`. The test server exposes a simple API that is used to enqueue responses and inspect the requests that it has received.

You can add the test server as a dev dependency using Composer.

```bash
composer require --dev guzzlehttp/test-server:^0.5
```

Alternatively, you can include it as a dev dependency in your project's existing composer.json file:

```json
{
    "require-dev": {
        "guzzlehttp/test-server": "^0.5"
    }
}
```

Any operation on the `Server` object will ensure that the server is running and wait until it is able to receive requests before returning.

`GuzzleHttp\Server\Server` provides a static interface to the test server. You can queue an HTTP response or an array of responses by calling `Server::enqueue()`. This method accepts an array of `Psr\Http\Message\ResponseInterface` and `Exception` objects.

```php
use GuzzleHttp\Client;
use GuzzleHttp\Psr7\Response;
use GuzzleHttp\Server\Server;

// Start the server and queue a response
Server::enqueue([
    new Response(200, ['Content-Length' => '0'])
]);

$client = new Client(['base_uri' => Server::$url]);
echo $client->request('GET', '/foo')->getStatusCode();
// 200
```

When a response is queued on the test server, the test server will remove any previously queued responses. As the server receives requests, queued responses are dequeued and returned to the request. When the queue is empty, the server will return a 500 response.

You can inspect the requests that the server has retrieved by calling `Server::received()`.

```php
foreach (Server::received() as $response) {
    echo $response->getStatusCode();
}
```

You can clear the list of received requests from the web server using the `Server::flush()` method.

```php
Server::flush();
echo count(Server::received());
// 0
```
