Simpletest module moved to a contributed module

SimpleTest module has been removed from core, and the core test runner will no longer run simpletests by itself.

Contributed modules with simpletest tests will see fatal errors on test discovery when testing against 9.0.x

However, simpletests can be successfully run in contrib using the following command to install the contrib simpletest module in drupalci.yml

      container_command:
        commands:
          - 'sudo -u www-data /usr/local/bin/composer require drupal/simpletest-simpletest dev-3.x --prefer-source --prefer-stable --no-interaction --working-dir /var/www/html'

Note that this command is subject to change as the contributed simpletest module develops, or may become unnecessary in the future if contrib simpletest support is added directly to DrupalCI.

Steps to add simpletest to your project

1. Download the drupalci.yml file to your project root and rename it drupalci.yml. Alternatively, from the command line, run curl https://www.drupal.org/files/drupalci.yml_.txt > drupalci.yml from your project root.
2. Commit it and push to drupal.org
3. You're done

Once you've converted all the simpletests in your project to PHPUnit you can remove the custom drupalci.yml file.

For more information on setting up a drupalci.yml see https://www.drupal.org/drupalorg/docs/drupal-ci/customizing-drupalci-tes...