[Mailer] Testing transport is broken using 7.2

[Fabrn]

Symfony version(s) affected

7.2.4

Description

Hello !

I've been trying to upgrade our project from 7.1.8 to 7.2.4, however, I'm getting an issue while running our test suites. We have a test that ensures that transport is defined using the X-Transport header. Even though the documentation says that the header is removed after sending the email, we could test the header like so :

$email = $this->getMailerMessage();

self::assertEmailHeaderSame($email, 'X-Transport', 'mailjet');

Now that I upgraded to 7.2.4, the header is removed. Then, I tried to test that the message was successfully sent using the mailjet transport using the transport parameter of the getMailerMessage method, but my message will not be returned.

The transport seems lost in test environment. Is it a bug ? Am I missing something ? Is there a better way to test the transport ?

How to reproduce

Setup a test multi-transport mailer configuration :

framework:
    mailer:
        transports:
            transport_a: '%env(MAILER_DSN_TRANSPORT_A)%'
            transport_b: '%env(MAILER_DSN_TRANSPORT_B)%'

Send a mail using a specific transport :

$message->getHeaders()->addTextHeader('X-Transport', 'transport_b');

$this->mailer->send($message);

Write a functional test checking for transport :

class MyTest extends KernelTestCase
{
    use MailerAssertionsTrait;

    public function test(): void
    {
        // send mail

        $email = $this->getMailerMessage();

        self::assertEmailHeaderSame($email, 'X-Transport', 'transport_b');
    }
}

Possible Solution

No response

Additional Context

No response

[xabbuh]

Can you create a small example application that allows to reproduce your issue?

[Fabrn]

Hello. Not for now but I can try my best to try it this evening

[Fabrn]

Hello there, sorry for being so late.

I've built my POC this morning, however I am not able to reproduce the issue yet. This might be something with our project.
I will try to look at this more closely and debug everything on Monday and I'm coming back to you with some news.

Have a nice day

[Fabrn]

Hello !

After investigating the issue, I found out that using Symfony 7.1, the Mailer::$transport property is initialized using the NullTransport in test environment, which is fine since DSN is null. NullTransport does not manipulate headers since AbstractTransport does not. However, simply by upgrading to 7.2, I found out that the Symfony\Component\Mailer\Transport\Transports replaces the NullTransport, which is a shame since it removes the header.

I think it is strange since our dsn are null://null, which is perfectly fine for 7.1 but not for 7.2. Is it something with DSN resolving ? Has anything changed for transport configuration ?

I am still investigating but I am already posting if anyone can help me here 😄

Thanks in advance