Add Docker-based test infrastructure

All three language suites now runnable without local toolchain installs.
- docker-compose.yml: node/ruby/php services with repo bind-mounted
- Makefile: test / test-node / test-ruby / test-php targets
- .devcontainer/devcontainer.json: VS Code universal image with all runtimes
- DEVELOPMENT.md: contributor guide

Validated by running all three suites in containers: 9 PHPUnit + 9 rspec
+ node:test all green. Fixes phpcs-aaa bootstrap (needed explicit
PHPCS autoload and Util\Tokens instantiation to define T_* polyfills).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: babu-ch

.devcontainer/devcontainer.json

@@ -0,0 +1,20 @@
+{
+  "name": "aaa-lint",
+  "image": "mcr.microsoft.com/devcontainers/universal:2-linux",
+  "features": {
+    "ghcr.io/devcontainers/features/node:1": { "version": "20" },
+    "ghcr.io/devcontainers/features/ruby:1": { "version": "3.2" },
+    "ghcr.io/devcontainers/features/php:1": { "version": "8.2" },
+    "ghcr.io/devcontainers/features/docker-in-docker:2": {}
+  },
+  "postCreateCommand": "npm install && (cd packages/rubocop-aaa && bundle config set --local path vendor/bundle && bundle install) && (cd packages/phpcs-aaa && composer install)",
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "dbaeumer.vscode-eslint",
+        "misogi.ruby-rubocop",
+        "bmewburn.vscode-intelephense-client"
+      ]
+    }
+  }
+}

.gitignore

@@ -1,5 +1,7 @@
 node_modules/
 dist/
+composer.lock
+.phpunit.result.cache
 .DS_Store
 *.log
 vendor/

DEVELOPMENT.md

@@ -0,0 +1,53 @@
+# Development
+
+This is a multi-language monorepo (JS / Ruby / PHP). To avoid requiring every contributor to install three toolchains locally, **all tests run inside Docker**.
+
+## Prerequisites
+
+- Docker + Docker Compose
+
+That's it. No local Node, Ruby, PHP, or Composer needed.
+
+## Running tests
+
+```bash
+make test          # all three languages
+make test-node     # eslint-plugin-aaa
+make test-ruby     # rubocop-aaa
+make test-php      # phpcs-aaa
+```
+
+Under the hood these run `docker compose run --rm <service>` against the services defined in `docker-compose.yml`:
+
+| Service | Image | Workdir |
+|---|---|---|
+| `node` | `node:20-alpine` | repo root (npm workspaces) |
+| `ruby` | `ruby:3.2-alpine` | `packages/rubocop-aaa` |
+| `php` | `composer:2` | `packages/phpcs-aaa` |
+
+The first run pulls images and installs dependencies into bind-mounted volumes (`node_modules`, `packages/rubocop-aaa/vendor/bundle`, `packages/phpcs-aaa/vendor`). Subsequent runs are fast.
+
+## Dev Container (optional)
+
+Opening the repo in VS Code with the Dev Containers extension will build a universal image pre-loaded with Node 20, Ruby 3.2, PHP 8.2, and Docker-in-Docker. See `.devcontainer/devcontainer.json`.
+
+## Running locally (without Docker)
+
+If you have the relevant toolchain installed you can also run tests directly:
+
+```bash
+# JS
+npm test --workspace=eslint-plugin-aaa
+
+# Ruby
+cd packages/rubocop-aaa && bundle install && bundle exec rspec
+
+# PHP
+cd packages/phpcs-aaa && composer install && composer test
+```
+
+## Cleaning up
+
+```bash
+make clean   # remove node_modules, vendor/, .bundle/
+```

Makefile

@@ -0,0 +1,17 @@
+.PHONY: test test-node test-ruby test-php clean
+
+test: test-node test-ruby test-php
+
+test-node:
+	docker compose run --rm node
+
+test-ruby:
+	docker compose run --rm ruby
+
+test-php:
+	docker compose run --rm php
+
+clean:
+	rm -rf node_modules packages/*/node_modules \
+	       packages/rubocop-aaa/vendor packages/rubocop-aaa/.bundle \
+	       packages/phpcs-aaa/vendor packages/phpcs-aaa/composer.lock

README.md

@@ -40,6 +40,14 @@ There is no built-in preset besides the English default. Use the `labels` option
 }
 ```
 
+## Development
+
+All tests run inside Docker — no local Node/Ruby/PHP installs required. See [DEVELOPMENT.md](./DEVELOPMENT.md).
+
+```bash
+make test          # run all three language suites
+```
+
 ## License
 
 MIT

docker-compose.yml

@@ -0,0 +1,22 @@
+services:
+  node:
+    image: node:20-alpine
+    working_dir: /work
+    volumes:
+      - .:/work
+    command: sh -c "npm install --silent && npm test --workspaces --if-present"
+
+  ruby:
+    image: ruby:3.2-alpine
+    working_dir: /work/packages/rubocop-aaa
+    volumes:
+      - .:/work
+    command: sh -c "apk add --no-cache build-base git && bundle config set --local path vendor/bundle && bundle install --quiet && bundle exec rspec"
+
+  php:
+    image: composer:2
+    working_dir: /work/packages/phpcs-aaa
+    volumes:
+      - .:/work
+    entrypoint: sh
+    command: -c "composer install --no-interaction --quiet && vendor/bin/phpunit"

packages/phpcs-aaa/tests/bootstrap.php

@@ -1,6 +1,9 @@
 <?php
 
 require __DIR__ . '/../vendor/autoload.php';
+require __DIR__ . '/../vendor/squizlabs/php_codesniffer/autoload.php';
+// PHPCS defines its T_* polyfill constants inside Util\Tokens; force-load it.
+new \PHP_CodeSniffer\Util\Tokens();
 
 if (!defined('PHP_CODESNIFFER_CBF')) {
     define('PHP_CODESNIFFER_CBF', false);