svelte-testing-library

Simple and complete Svelte testing utilities that encourage good testing practices.

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The problem
This solution
Example
Installation
Guiding Principles
Contributors
Docs
Issues
LICENSE

The problem

You want to write maintainable tests for your Svelte components. As a part of this goal, you want your tests to avoid including implementation details of your components and rather focus on making your tests give you the confidence for which they are intended. As part of this, you want your testbase to be maintainable in the long run so refactors of your components (changes to implementation but not functionality) don't break your tests and slow you and your team down.

This solution

The svelte-testing-library is a very lightweight solution for testing Svelte components. It provides light utility functions on top of svelte and dom-testing-library, in a way that encourages better testing practices. Its primary guiding principle is:

The more your tests resemble the way your software is used, the more confidence they can give you.

Example

You can check the live example at CodeSandbox, "Browser" tab renders App.svelte and "Tests" tab runs App.spec.js

Live demo: https://codesandbox.io/s/live-demo-svelte-testing-library-q8iv7

App.svelte

<script>
  export let name

  let buttonText = "Button Text";

  function handleClick() {
    buttonText = "Button Clicked";
  }
</script>

<style>
  h1 {
    color: purple;
  }
</style>

<h1>Hello {name}!</h1>

<button on:click={handleClick}>{buttonText}</button>

App.spec.js

import App from "./App.svelte";
import {
  render,
  cleanup,
  fireEvent,
  waitForElement
} from "@testing-library/svelte";
import "@testing-library/jest-dom/extend-expect";

afterEach(cleanup);

describe("App", () => {
  test("should render greeting", () => {
    const { getByText } = render(App, { props: { name: "world" } });

    expect(getByText("Hello world!"));
  });

  test("should change button text after click", async () => {
    const { getByText } = render(App, { props: { name: "world" } });

    fireEvent.click(getByText("Button Text"));

    const button = await waitForElement(() => getByText("Button Clicked"));

    expect(button).toBeInTheDocument();
  });
});

Installation

This module is distributed via npm which is bundled with node and should be installed as one of your project's devDependencies:

npm install --save-dev @testing-library/svelte

This library has peerDependencies listings for svelte.

You may also be interested in installing jest-dom so you can use the custom jest matchers.

Docs

Guiding Principles

The more your tests resemble the way your software is used, the more confidence they can give you.

We try to only expose methods and utilities that encourage you to write tests that closely resemble how your svelte components are used.

Utilities are included in this project based on the following guiding principles:

If it relates to rendering components, it deals with DOM nodes rather than component instances, nor should it encourage dealing with component instances.
It should be generally useful for testing individual Svelte components or full Svelte applications.
Utility implementations and APIs should be simple and flexible.

At the end of the day, what we want is for this library to be pretty light-weight, simple, and understandable.