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

Adding an API endpoint for saving data

In this section, we’ll start by adding the POST request handler function for saving data and then continue with the PUT function, in its own route file, for updating data.

Let’s begin with a test helper:

  1. Create a new file, src/factories/request.js, with the following content. This will be used by both the POST and PUT functions to read the data of the request. SvelteKit will pass a Request argument. The only bit of this we need to provide is the json method, as shown here:
    export const createRequest = (json) => ({
      json: () => Promise.resolve(json)
    });

Providing minimal versions of collaborating objects

SvelteKit passes the Request objects into our request handler functions. But for our unit tests we don’t need fully formed Request objects, we just need an object that implements the parts of the interface that we use. Our application code doesn’t use anything but the json method...