Drupal 8 Forms and TDD, part 1: file validation

Traditionally, testing Drupal forms has mainly consisted of testing the form through the UI using functional tests. However, with the revamp of the Forms API to a fully OO paradigm, using unit tests has now become much easier.

Using TDD when writing a form requires us to think a little bit differently about our code, compared to a more traditional approach. In this example, I'll consider a form with 3 particularities :

• a CSV file upload with a custom validation callback
• a field that only appears for users with a certain permission
• a text field with a format validation

Furthermore, upon submission, we will parse the CSV file and create new entities. I'll treat this as a series of posts. In this first post, we'll look how to get set up, and how to use TDD when writing a custom file validation callback.

Links

• Part 2.
• Part 3.
• Part 4.
• The source code for the example.
• The Composer template for Drupal project used for the project structure.
• The official documentation for writing automated tests in Drupal 8.