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

Clearing the data store between tests

It turns out our tests are not independent: changes to the db object in one test affect the other tests, too. We have to clear down our test database between each run. We can solve that by creating a clear function that will clear the database object, and we’ll use a beforeEach block to call it before every test.

What we need is the clear function that we can call directly in our tests. However, if you try to add this function to the +page.server.js file, you’ll get a warning from SvelteKit when you run your Playwright tests:

Error: Invalid export 'clear' in /birthdays (valid exports are load, prerender, csr, ssr, actions, trailingSlash, or anything with a '_' prefix)

Why does this error appear only in the Playwright tests and not the Vitest tests? Your Vitest tests do not run through the SvelteKit server code, so the framework has no opportunity to check for invalid exports. It’s only when you...