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

Implementing the negated matcher

Negating a matcher is a tricky business, mainly because negated matchers can have confusing meanings. For example, what does the following expectation mean?

expect(result).not.toBeUnprocessableEntity({
  error: 'An unknown ID was provided.'
});

Presumably, it should fail if the response is 422 and the response body matches the object provided. But should it also fail if the response is, say, a 500 or 200 response? If that was what was expected, wouldn’t it be enough to write this?

expect(result).not.toBeUnprocessableEntity();

I find that when writing matchers for domain-specific ideas, negated matchers are best avoided, or at least restricted in their use. However, to show how it’s done, let’s carry on with the matcher.

When we negate the matcher, the Vitest test runner will fail the test if the matcher returns a pass value of true. We have exactly one scenario where this occurs, as all our guard...