feat: install ParaTest in the image

ARCHITECTURE.md

@@ -32,7 +32,7 @@ phpqa/
 ### 1. Image Docker (`Dockerfile`)
 
 Image Docker construite en deux étapes (`php:X.Y-cli` pour compiler, `debian:slim` à l'exécution) avec :
-- Uniquement les outils QA appelés par les tâches Castor (PHPStan, ECS, Rector, Deptrac, PHPUnit, Infection, parallel-lint, Mago)
+- Uniquement les outils QA appelés par les tâches Castor (PHPStan, ECS, Rector, Deptrac, PHPUnit, ParaTest, Infection, parallel-lint, Mago)
 - Castor pré-installé (binaire statique)
 - Les extensions PHP nécessaires aux projets Symfony/Doctrine
 - Le layout `/tools/.composer/vendor-bin/...` hérité de `jakzal/phpqa`, référencé par les projets

Dockerfile

@@ -122,9 +122,22 @@ COPY <<EOF /tools/.composer/vendor-bin/infection/composer.json
 }
 EOF
 
+# paratest runs the test files in parallel processes and merges the coverage of its workers itself,
+# which is what sharding a suite across CI jobs cannot do: PHPUnit does not merge XML coverage
+# reports from several runs. It is a Composer package and needs phpunit/phpunit in its own vendor
+# tree, which is usually what makes it awkward beside a PHAR; this tree already holds one, pulled by
+# the extensions it exists for.
+#
+# "^7" rather than a precise version, because the PHP of the build is what decides: paratest 7.26
+# asks for PHP 8.4 and PHPUnit 13.4, 7.20 for PHP 8.3 and PHPUnit 12.5, 7.8 for PHP 8.2 and PHPUnit
+# 11.5. Composer resolves the newest that runs here, and the PHPUnit it brings is the newest that
+# runs here too, which is the same bound the PHAR loop further down uses to pick /tools/phpunit. So
+# the Composer PHPUnit of this tree and that PHAR land on the same version on every PHP the image is
+# built for, and pinning either one is what would make them disagree.
 COPY <<EOF /tools/.composer/vendor-bin/phpunit/composer.json
 {
     "require": {
+        "brianium/paratest": "^7",
         "digitalrevolution/phpunit-extensions": "^1.13",
         "ergebnis/phpunit-slow-test-detector": "^2.24",
         "symfony/browser-kit": "^6.4|^7.0|^8.0",
@@ -143,7 +156,8 @@ RUN set -eux; \
 	ln -s /tools/.composer/vendor-bin/phpstan/vendor/bin/phpstan /tools/phpstan; \
 	ln -s /tools/.composer/vendor-bin/ecs/vendor/bin/ecs /tools/ecs; \
 	ln -s /tools/.composer/vendor-bin/rector/vendor/bin/rector /tools/rector; \
-	ln -s /tools/.composer/vendor-bin/infection/vendor/bin/infection /tools/infection
+	ln -s /tools/.composer/vendor-bin/infection/vendor/bin/infection /tools/infection; \
+	ln -s /tools/.composer/vendor-bin/phpunit/vendor/bin/paratest /tools/paratest
 
 # ------------------------------------------------------------
 # PHAR tools + Castor

README.md

@@ -3,7 +3,7 @@
 This repository provides:
 
 1. **🐳 Lean Docker Image** (~800 MB, ~150 MB compressed) built on the official `php:X.Y-cli` images with:
-   - ✅ Only the QA tools used by the Castor tasks (PHPStan, ECS, Rector, Deptrac, PHPUnit, Infection, parallel-lint, Mago)
+   - ✅ Only the QA tools used by the Castor tasks (PHPStan, ECS, Rector, Deptrac, PHPUnit, ParaTest, Infection, parallel-lint, Mago)
    - 🛠️ [Castor](https://github.com/jolicode/castor) pre-installed as a task runner (static build, works on every PHP version)
    - 🧩 The PHP extensions needed by Symfony/Doctrine projects (intl, pdo_pgsql, redis, amqp, imagick, xdebug, ...)
    - 🧪 Enhanced PHPUnit, PHPStan, and Infection tooling
@@ -123,6 +123,7 @@ ship its own copy in `vendor/bin`:
 | `rector` | `/tools/.composer/vendor-bin/rector` |
 | `infection` | `/tools/.composer/vendor-bin/infection` |
 | `deptrac`, `composer normalize` | `/tools/.composer/vendor` |
+| `paratest` (parallel PHPUnit, merges the coverage of its workers) | `/tools/.composer/vendor-bin/phpunit` |
 | PHPUnit helpers (slow test detector, foundry, browser-kit, ...) | `/tools/.composer/vendor-bin/phpunit` |
 | `phpunit-10` … `phpunit-13` (PHAR), `phpunit` → newest one supported by the PHP version | `/tools` |
 | `parallel-lint` (PHAR) | `/tools` |