Writing a kernel test

Let’s build upon the previous example. Assume now that stakeholders have asked you to output a field value on the screen in the camel case format. The good news is we have a working implementation and unit test, so we can make short work of this task in Drupal.

In this case, we need to make a field formatter class for string fields. When the formatter is used on a field to display output, we want to run the user input through our existing CamelCase class. If you need a refresher on field formatters and managing entity displays, refer to Chapter 2, Content Building Experience.

This provides an excellent example to step into a kernel test. Earlier, we mentioned that kernel tests create a minimal installation of Drupal with the setup that you specify in your test, in order to run and evaluate their test methods. There is no danger in running kernel tests, as they do not touch or interfere with your current site database in any way. When the test is done...