Writing a unit test
Let’s write our first test. As previously mentioned, a unit test is the lowest-level type of test you can write. It only executes and tests raw PHP code that has no dependencies on services such as a connected database or other integrated APIs. This means the test can execute using PHP only.
Getting ready
Let’s create a scenario that will help you think about when and how to apply unit testing. Imagine you have to provide data to a frontend component. The frontend developer has requested that you provide all JSON keys in camelCase format in the API response. camelCase would turn strings such as field_event_date into fieldEventDate.
snake_case is used in many places in Drupal; the most common place you will see this is with machine names (such as on the preceding event date field). All machine names in Drupal are in snake_case.
This is a very simple example but perfect to illustrate how we can wield a unit test to test our class.