Symfony custom tests namespace not working

Question

I want to configure a custom namespace for my tests but I get an error when lauching composer install in prod env

Here relevants parts of my config :

# config/services.yaml

    Tests\:
        resource: '../tests/'
        exclude: '../tests/bootstrap.php'

# composer.json
    "autoload": {
        "psr-4": {
            "App\\": "src/",
            "App\\Fixtures\\" : "fixtures/",
            "SymfonyStandard\\": "_archives/app/SymfonyStandard/"
        }
    },
    "autoload-dev": {
        "psr-4": {
            "Tests\\": "tests/"
        }
    },

# tests/AbstractWebTest.php

namespace Tests;

[...]

abstract class AbstractWebTest extends WebTestCase
{
}

The error I get whith composer

$ composer install --no-dev --optimize-autoloader

!!  In FileLoader.php line 174:
!!                                                                                 
!!    Expected to find class "Tests\AbstractWebTest" in file "/project_dir/tests/AbstractWebTest.php" while importing services from resource   
!!    "../tests/", but it was not found! Check the namespace prefix used with the  
!!     resource in /project_dir/config/services.yaml (which is being
!!    imported from "/project_dir/src/Kernel.php").              
!!                                                                                 
!!  
!!  In FileLoader.php line 224:
!!                                                                                 
!!    Expected to find class "Tests\AbstractWebTest" in file "/project_dir/tests/AbstractWebTest.php" while importing services from resource   
!!    "../tests/", but it was not found! Check the namespace prefix used with the  
!!     resource.                                                                   

Note : src/Kernel.php is the default file with no changes

What I already tried :

• resource: '../tests/*'
• remove abstract from class
• remove Test suffix from class
• exclude class in services.yaml (I get same error at next file)