[meta] Improve test coverage

The Drupal community has deprecated SimpleTest and the Webform module needs to switch over using PHPUnit (https://www.drupal.org/docs/8/phpunit) based tests.

Concepts

• Tests confirm expectations.
• Tests should be repeatable, maintainable, and easy to execute
• Tests are documentation.

Notes

• Webform module requires that all features, functionality and even form elements have an example/test page that developer or an automated test can review and fix expecting
• Simple test has better ui integration but is deprecated.
• JavaScript testing is now supported

Things that don't need 100% test coverage.

• Features that extend core systems which already include test coverage
• Features that are too time consuming to write tests for, especially if it is less time and effort to assume that users and developer will create issues if the feature fails to meet expectations.

Features that lack good test coverage

• Translations
• States API JS
• Webform fields

Tasks

• Setup Drupal\Tests\BrowserTestBase example
• Setup WebformBrowserTestBase
• Setup Webform loader.

References

• https://www.drupal.org/docs/8/phpunit
• https://www.drupal.org/docs/8/phpunit/running-phpunit-tests
• https://www.drupal.org/docs/8/phpunit/phpunit-browser-test-tutorial
• https://docs.acquia.com/article/lesson-104-phpunit-doubles-mocks-stubs
• http://softpixel.com/~mradcliffe/files/dco2015-mocking-drupal.pdf
• http://www.pixelite.co.nz/article/writing-phpunit-tests-for-your-custom-...
• https://www.previousnext.com.au/blog/drupal-8-ftw-it-test-or-it-form-act...
• https://www.chapterthree.com/blog/javascript-testing-comes-to-drupal-8
• https://www.phase2technology.com/blog/ajax-testing-in-drupal-8/