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

Using a component mock library

In the last chapter, you saw how you can use vi.fn to spy on functions. The svelte-component-double npm package can be used in a similar fashion, achieving the same effect as the hand-rolled mocks you’ve just learned about.

The package includes matchers such as toBeRendered and toBeRenderedWithProps to check that the component is indeed rendered in the way you wanted.

Let’s split this into a couple of parts: installing the library and writing tests.

Installing the library

The library requires a bit of setup to get the relevant matchers into place:

  1. Run the following command to install the package:
    npm install --save-dev svelte-component-double
  2. Then, create a new file named src/vitest/registerSvelteComponentDouble.js with the following content. It registers the matchers and also gives us global access to the componentDouble function, which is not required but makes mock setup easier:
    import { expect } from 'vitest...