Thanks for the PR 😍

How to test these changes in your application

1. Define the SYMFONY_ENDPOINT environment variable:

   # On Unix-like (BSD, Linux and macOS)
   export SYMFONY_ENDPOINT=https://raw.githubusercontent.com/symfony/recipes/flex/pull-1071/index.json
   # On Windows
   SET SYMFONY_ENDPOINT=https://raw.githubusercontent.com/symfony/recipes/flex/pull-1071/index.json

2. Install the package(s) related to this recipe:

   composer req 'symfony/flex:^1.16'
   composer req 'symfony/mailer:^4.3'

3. Don't forget to unset the SYMFONY_ENDPOINT environment variable when done:

   # On Unix-like (BSD, Linux and macOS)
   unset SYMFONY_ENDPOINT
   # On Windows
   SET SYMFONY_ENDPOINT=

Diff between recipe versions

In order to help with the review stage, I'm in charge of computing the diff between the various versions of patched recipes.
I'm going keep this comment up to date with any updates of the attached patch.

We could simply update the .env.test and add the line MAILER_DSN=null://null, no?

I don't believe the recipe can update .env.test, can it? Or are you suggesting adding to the phpunit/phpunit-bridge recipes?

I don't believe the recipe can update .env.test, can it?

Yeah it looks like it can: https://github.com/symfony/recipes/blob/master/phpunit/phpunit/4.7/manifest.json#L3

Or are you suggesting adding to the phpunit/phpunit-bridge recipes?

Yes, and in the phpunit/phpunit recipe too!

But that was just a suggestion, I don't know what solution prefers the core team 👀

Yeah it looks like it can

I meant add a single line to the .env.test file.

But that was just a suggestion

Both achieve the same thing, doesn't matter to me. Adding the the phpunit/phpunit-bridge recipes seems simpler.

I modified this PR to just always use null://null instead of smtp://localhost. I feel it rather unlikely someone has a local mail server. The docker integration is unaffected by this.