.gitlab-ci.yml

cache:
  paths:
    - vendor/

before_script:
  # Install Docker
  - bash ci/docker_install.sh > /dev/null

  # Install SSH
  - 'which ssh-agent || ( apt-get update -y && apt-get install openssh-client -y )'
  - eval $(ssh-agent -s)
  - echo "$SSH_PRIVATE_KEY" | tr -d '\r' | ssh-add -
  - mkdir -p ~/.ssh
  - chmod 700 ~/.ssh
  - ssh-keyscan gitlab.com >> ~/.ssh/known_hosts
  - chmod 644 ~/.ssh/known_hosts

  # Setup git
  - git config --global user.email "wgroenewold@gmail.com"
  - git config --global user.name "Gitlab CI"

  # Setup composer
  - 'which wget || ( apt-get update -y && apt-get install wget -y )'
  - wget https://composer.github.io/installer.sig -O - -q | tr -d '\n' > installer.sig
  - php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
  - php -r "if (hash_file('SHA384', 'composer-setup.php') === file_get_contents('installer.sig')) { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
  - php composer-setup.php
  - php -r "unlink('composer-setup.php'); unlink('installer.sig');"
  - php composer.phar install

  - git clone -b master https://github.com/WordPress/WordPress-Coding-Standards.git /usr/local/bin/wpcs

stages:
  - test  

test:7.2:
  image: php:7.2
  script:
    # PHP Syntax check
    - find . -path ./vendor -prune -o -name '*.php' -print0 | xargs -0 -n 1 -P 4 php -l
    # PHPCS
    - find . -path ./vendor -prune -o -name '*.php' -print0 | xargs -0 -n 1 -P 4 /usr/local/bin/phpcs --runtime-set ignore_warnings_on_exit 1  

test:5.6:
  image: php:5.6
  script:
    # PHP Syntax check
    - find . -path ./vendor -prune -o -name '*.php' -print0 | xargs -0 -n 1 -P 4 php -l
    # PHPCS
    - find . -path ./vendor -prune -o -name '*.php' -print0 | xargs -0 -n 1 -P 4 /usr/local/bin/phpcs --runtime-set ignore_warnings_on_exit 1    

README.md

Create a separate SSH key pair with ssh-keygen for CI.

Go to your project’s Settings > CI/CD and expand the Variables section. Click the Add Variable button. In the Add variable modal, fill in the details:

Key = SSH_PRIVATE_KEY

docker-install.sh

#!/bin/bash

# We need to install dependencies only for Docker
[[ ! -e /.dockerenv ]] && exit 0

set -xe

# Install git
apt-get update -yqq
apt-get install git -yqq

# Install PHPCS
curl --location --output /usr/local/bin/phpcs https://squizlabs.github.io/PHP_CodeSniffer/phpcs.phar
curl --location --output /usr/local/bin/phpcbf https://squizlabs.github.io/PHP_CodeSniffer/phpcbf.phar
chmod +x /usr/local/bin/phpcs
chmod +x /usr/local/bin/phpcbf

# Install mysql driver
# Here you can install any other extension that you need
docker-php-ext-install pdo_mysql