test: add Docker-based test suite for setup scripts

[hermes-denkobot]

Summary

Adds a Docker-based integration test suite for the machine setup automation scripts. Every test runs inside a disposable Ubuntu 24.04 container with systemd — zero impact on the host system.

Features

• Container lifecycle management — Reusable functions to create, manage, and destroy test containers
• Assertion library — Functions for checking packages, services, config files, and group membership
• Idempotency testing — Framework that runs each script twice to verify idempotency
• Integration tests for: setup-basics, setup-docker, setup-sshd, configure-firewall
• BATS unit tests for the shared helpers library
• ShellCheck static analysis in the main runner

Test Architecture

tests/
├── lib/
│   ├── container-manager.sh   # Container lifecycle
│   └── test-helpers.sh        # Assertion library
├── unit/
│   └── test-helpers.bats      # BATS unit tests
└── integration/
    ├── test-basics.sh
    ├── test-docker.sh
    ├── test-sshd.sh
    └── test-firewall.sh

Usage

./tests/run-all.sh              # Run everything
./tests/run-integration.sh test-docker   # Single test
./tests/run-all.sh unit         # Static analysis only

How It Works

1. Spins up a fresh ubuntu:24.04 --privileged container with systemd
2. Copies the repo into the container
3. Creates a test user with passwordless sudo
4. Runs the setup script
5. Asserts: packages installed, services running, config correct
6. Runs the script a second time to verify idempotency
7. Tears down the container (logs captured on failure)