Add ResponseIsUnprocessable assertion

[garak]

Description
Now that we got an automatic way to get 422 response code when a form is invalid (see #40799), I think it could be nice to ease testing it.
I'm proposing to add a new method to BrowserKitAssertionsTrait:

<?php

namespace Symfony\Bundle\FrameworkBundle\Test;

trait BrowserKitAssertionsTrait
{
    public static function assertResponseIsUnprocessable(string $message = ''): void
    {
        self::assertThatForResponse(new ResponseConstraint\ResponseIsUnprocessable(), $message);
    }
    // ...
}

with relative constraint

<?php

namespace Symfony\Component\HttpFoundation\Test\Constraint;

use PHPUnit\Framework\Constraint\Constraint;
use Symfony\Component\HttpFoundation\Response;

final class ResponseIsUnprocessable extends Constraint
{
    /**
     * {@inheritdoc}
     */
    public function toString(): string
    {
        return 'is unprocessable';
    }

    /**
     * @param Response $response
     *
     * {@inheritdoc}
     */
    protected function matches($response): bool
    {
        return Response::HTTP_UNPROCESSABLE_ENTITY === $response->getStatusCode();
    }

    /**
     * @param Response $response
     *
     * {@inheritdoc}
     */
    protected function failureDescription($response): string
    {
        return 'the Response '.$this->toString();
    }

    /**
     * @param Response $response
     *
     * {@inheritdoc}
     */
    protected function additionalFailureDescription($response): string
    {
        return (string) $response;
    }
}

Example

Instead of calling self::assertResponseStatusCodeSame(422) or self::assertResponseStatusCodeSame(Response::HTTP_UNPROCESSABLE_ENTITY) each time that you want to test for a submitted invali form, you could simply call self::assertResponseIsUnprocessable()

[carsonbot]

Thank you for this suggestion.
There has not been a lot of activity here for a while. Would you still like to see this feature?

[garak]

Thank you for this suggestion. There has not been a lot of activity here for a while. Would you still like to see this feature?

I do.

[fabpot]

Please, go ahead and create a PR.