Book Image

Svelte with Test-Driven Development

By : Daniel Irvine
Book Image

Svelte with Test-Driven Development

By: Daniel Irvine

Overview of this book

Svelte is a popular front-end framework used for its focus on performance and user-friendliness, and test-driven development (TDD) is a powerful approach that helps in creating automated tests before writing code. By combining them, you can create efficient, maintainable code for modern applications. Svelte with Test-Driven Development will help you learn effective automated testing practices to build and maintain Svelte applications. In the first part of the book, you’ll find a guided walkthrough on building a SvelteKit application using the TDD workflow. You’ll uncover the main concepts for writing effective unit test cases and practical advice for developing solid, maintainable test suites that can speed up application development while remaining effective as the application evolves. In the next part of the book, you’ll focus on refactoring and advanced test techniques, such as using component mocks and writing BDD-style tests with the Cucumber.js framework. In the final part of the book, you’ll explore how to test complex application and framework features, including authentication, Svelte stores, and service workers. By the end of this book, you’ll be well-equipped to build test-driven Svelte applications by employing theoretical and practical knowledge.
Table of Contents (22 chapters)
1
Part 1: Learning the TDD Cycle
8
Part 2: Refactoring Tests and Application Code
16
Part 3: Testing SvelteKit Features

Validating Form Data

Now that our system is accepting new birthdays, we need to validate the data coming in. In this chapter, we’ll see how we can test-drive the SvelteKit fail function to return useful information to the user so that they can correct any errors.

Figure 5.1 shows what is displayed to the user after the server has deemed their date of birth invalid. Notice how the invalid form data is maintained so that the user has a chance to correct it:

Figure 5.1 – A validation error is shown when entering an invalid date

Figure 5.1 – A validation error is shown when entering an invalid date

This chapter covers the following key topics:

  • Adding a Playwright test for validating form errors
  • Displaying SvelteKit form errors
  • Validating data in the form action
  • Clearing the data store between tests

By the end of the chapter, you’ll have a good understanding of how to implement form validation using a test-driven approach.