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

Providing extra information in failure messages

This section improves the detailed information that is presented to the developer when a test fails. The purpose of this extra information is to help pinpoint the issue with the application code so that the developer isn’t left scratching their head about what went wrong.

Let’s begin:

  1. Add the next test, which checks that a basic message is shown when the response bodies do not match:
    it('returns a message if the provided object does not match', () => {
      const response = fail(422, { a: 'b' });
      expect(() =>
        expect(response).toBeUnprocessableEntity({
          c: 'd'
        })
      ).toThrowError(/Response body was not equal/);
    });
  2. To make that pass, add the message property to the second guard clause return value. We’ll expand on this in the next test:
    if (!this.equals(.....