Document local test usage

CONTRIBUTING.md

@@ -0,0 +1,53 @@
+# Contributing
+
+Features and bug fixes are welcome! First-time contributors can jump in with the issues tagged [good first issue](https://github.com/jhedstrom/drupalextension/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22).
+
+## Testing
+
+Testing is performed automatically in Github Actions when a PR is submitted. To execute tests locally before submitting a PR, you'll need [Docker and Docker Compose](https://docs.docker.com/engine/install/).
+
+Configure your local test environment:
+```
+export PHP_VERSION=8.1
+export DRUPAL_VERSION=10
+export DOCKER_USER_ID=${UID}
+```
+
+Prepare your local environment for testing:
+```
+docker-compose up -d
+docker-compose exec -T -u node node npm install
+docker-compose exec -T php composer self-update
+docker-compose exec -u ${DOCKER_USER_ID} -T php composer require --no-interaction --dev --no-update drupal/core:^${DRUPAL_VERSION} drupal/core-composer-scaffold:^${DRUPAL_VERSION}
+docker-compose exec -T php composer install
+docker-compose exec -T php ./vendor/bin/drush --yes --root=drupal site-install --db-url=mysql://drupal:drupal@db/drupal --debug
+docker-compose exec -T php cp -r fixtures/drupal/modules/behat_test drupal/modules
+docker-compose exec -T php ./vendor/bin/drush --yes --root=drupal pmu page_cache
+docker-compose exec -T php ./vendor/bin/drush --yes --root=drupal en behat_test
+```
+
+Execute NPM linters:
+```
+docker-compose exec -T -u node node npm test
+```
+
+Execute PHP checks:
+```
+docker-compose exec -T php composer test
+```
+
+Execute Behat tests:
+```
+docker-compose exec -T php vendor/bin/behat -fprogress --strict
+docker-compose exec -T php vendor/bin/behat -fprogress --profile=drupal --strict
+```
+
+Execute specific tests, eg just PHPUnit's Drupal7FieldHandlerTest:
+```
+docker-compose exec -T php vendor/bin/behat -fprogress --profile=drupal --strict --tags=@random
+```
+
+## Before submitting a change
+
+- Check the changes from `composer require` are not included in your submitted PR.
+- Before testing another PHP or Drupal version, revert changes to `composer.json` and remove `composer.lock`, `package-lock.json`, `drupal/`, and `vendor/`.

README.md

@@ -102,3 +102,5 @@ See [CHANGELOG](CHANGELOG.md).
 
 Features and bug fixes are welcome! First-time contributors can jump in with the
 issues tagged [good first issue](https://github.com/jhedstrom/drupalextension/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22).
+
+See [CONTRIBUTING.md](https://github.com/jhedstrom/drupalextension/blob/master/CONTRIBUTING.md) for more information.