[HttpClient][DI] Add an option to use the MockClient in functional tests

[GaryPEGEOT]

Q	A
Branch?	master
Bug fix?	no
New feature?	yes
Deprecations?	no
Tickets
License	MIT
Doc PR	TODO

Let's say you want to mock HTTP responses in your test or dev environment:

First, you create an invokable class responsible of generating the response:

namespace App\Tests;

use Symfony\Contracts\HttpClient\ResponseInterface;

class MyAwesomeCallback
{
    public function __invoke(string $method, string $url, array $options = []): ResponseInterface
    {
        // load a fixture file or generate dynamic data
    }
}

Then configure it:

# config/services_test.yaml
services:
   # ...
   App\Tests\MyAwesomeCallback: ~

# config/packages/test/framework.yaml
framework:
    http_client:
        mock_response_factory: App\Tests\MyAwesomeCallback

The HttpClient will now be using MockHttpClient in your functional test:

$client = static::createClient();

// No live HTTP connection made
$client->request('GET', '/path-with-http-call');

[nicolas-grekas]

Very related to #35651 and #35677

[fabpot]

@nicolas-grekas Can you have a look at this one as it would unblock some other PRs as well?

[nicolas-grekas]

LGTM, I just have minor notes.

[fabpot]

Thank you @GaryPEGEOT.