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Styling Components

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What you'll learn​
  • Why you should test your component's styles
  • How to render components correctly with their CSS styles
  • How to handle 3rd party CSS libraries

Why Test Your Component's Styles?​

Stylesheets are a critical part of your component's business logic. One of the best examples of this is a modal component. Common modal bugs include: z-index issues, inability to dismiss the overlay, and inability to interact with the parent page after dismissing the modal.

Node-based test runners like Jest or Vitest can't catch these kinds of issues because they render your styles in emulated DOM environments like JSDom. JSDom doesn't have a box model and certain kinds of assertions, such as if a parent is covering a child and preventing clicks, are not possible to test without a more realistic environment.

On the other hand, browser-based runners like Cypress allow you to render your application's styles and components and allow Cypress's Driver to take advantage of the real box-model and style rendering engine. Cypress's commands like cy.click and assertions like should('be.visible') have business logic that makes sure the UI you're trying to assert on and interact with is visible and interactible for your end users. This is a benefit unique to browser-based test runners.

Rendering Components Correctly​

The first time you mount any new component, you may notice that the component doesn't look like it should. Unless your application is written exclusively using Component-scoped CSS (e.g. Styled Components or Vue's Scoped Styles) you will need to follow this guide in order to get your component looking and behaving like it will in production.

tip

Ensure that whatever you're doing in production is happening within either the Component HTML file or the Component Support File.

Component Support File​

When you load a component or end-to-end spec file, it will first load something called a supportFile. By default, this is created for you during first-time setup of Cypress Component Testing and is located at cypress/support/component.js. This file gives you the opportunity to set up your spec's environment.

For component specs, you use this file to set up page-level concerns that would usually exist by the time you mount the component. Some examples include:

  1. Run-time JavaScript code (state management, routers, UI libraries)
  2. Global styles (style resets, Tailwind)

As a rule, your Component Support File should look very similar to your application's main JavaScript (ie: main.js, index.js) and main CSS (ie: main.css, index.css) files.

3rd Party CSS Libraries (Tailwind, Bootstrap, PopperJS)​

Components can have three parts: markup, styles, and script logic. All three of these work together in order to deliver a working component.

Styles are business logic, too.

  1. Tailwind
  2. CSS Modules
  3. Scoped Styled
  4. Styled Components
  5. Regular Stylesheets
  6. UI Libraries

This guide will help you setup your test infrastructure to render your component's styles properly.

Depending on how your application is built, the first time you mount a new component, it may be completely or somewhat unstyled.

This makes sense. Many applications have some amount of one-time setup that is run outside of the component file.

We build our applications within the context that they're supposed to run in, and we make assumptions that our components will always be rendered within a root-level component (such as an <App>) or a top-level selector with style rules (such as #app { /* styles in here */ } )

When we attempt to isolate our component to put it under test, we need to put that environment back together. We'll go into that in a moment. First, let's talk about stylesheets, testing, and one of Cypress's biggest differences in contrast to other component testing tools.

Importing Stylesheets​

Each application or component library imports styles a little differently. We'll go over a few methods and describe how you can quickly restructure your components to become more testable.

If you do not follow this guide, your components will mount, but they won't look correct and you may not be able to benefit from some of the most valuable parts of Cypress. Namely, implicit checks for width, height, and overflow to ensure that your components not only exist in the page's HTML but are also visible.

Rules for Setting Up Your Styles​

All of your application's styles need to end up in Cypress so that when your component mounts, it looks right.

We expose two hooks for you to configure your styles:

  1. An HTML file called cypress/support/component-index.html
  2. A JavaScript support file called cypress/support/component.js

When creating a production-like test environment, you should always mimic your own application's setup. If your application has multiple <link> tags to load fonts or other stylesheets within the head, ensure that the cypress/support/component-index.html file contains the same <link> tags. The same logic follows for any styles loaded in your Application's main.js file. If you import a ./styles.css at the top of your main.js file, make sure to import it in your cypress/support/component.js file.

For this reason, it's strongly suggested to make a src/setup.js file that will be re-used in your main.js entrypoint as well as in your test setup. An example project structure would look like so:

> /cypress
>   /support
>    /component.js
> /src
>  /main.js
>  /main.css
>  /setup.js

The contents of setup.js may look like so:

import '~normalize/normalize.css'
import 'font-awesome'
import './main.css'

export const createStore = () => {
  return /* store */
}

export const createRouter = () => {
  return /* router */
}

export const createApp = () => {
  return <App router={createRouter()} store={createStore()}></App>
}

and its usage in main.js could look like so:

import { createApp } from './setup.js'

ReactDOM.render(createApp())

and Cypress would re-use it in its support file

/* And that's it! */
import '../../src/setup.js'

The rest of this section is dedicated to discussing specific style problems you may have, including: Fonts, Icon Fonts, Style Resets, Global App Styles, and 3rd party component library styles.

Global App Styles​

Your global application styles are usually in one of the following places:

  1. A styles.css file you import within the head of your application.

This should be loaded within your Cypress Index HTML file.

  1. Within a root-level component like App.jsx, App.vue, App.svelte, etc.

Decouple your Root CSS from your App or Entrypoint component by pulling out these global styles into a top-level stylesheet. Both Vue and Svelte embed global application styles into the main entry point components. The rest of your application expects to be rendered within those components, and so any assumptions you made when writing those components must be replicated in your test environment or else your components won't look right.

<style>
  /* In certain scaffolds, the App.vue file does not have a separate styles file */

  #app {
    font-family: Sans-serif;
  }
</style>

Should become

/* App.vue */ <style src="./app.css" />

and

/* cypress/support/component.js */ import '../../src/app.css'
  1. Within the main.js file of your application (which subsequently mounts your root-level component).

Re-using stylesheets that are imported in the beginning of your application was covered in the last section.

import './main.css'
  1. Within a configuration file like next.config.js or nuxt.config.js.

You're usually providing public paths to these stylesheets. You can import the same paths within your cypress/support/component-index.html file.

CSS Reset or Normalize isn't applied​

Are you importing your normalize file within cypress/support/component-index.html or within cypress/support/component.js?

Fonts: Everything is rendering in Times New Roman​

Most applications handle fonts in one of two ways.

  1. Your index.html loads external fonts in the head tag.
<head>
  <link rel="preconnect" href="https://fonts.googleapis.com" />
  <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
  <link
    href="https://fonts.googleapis.com/css2?family=Readex+Pro:wght@200;300;400;500;600;700&family=Roboto&display=swap"
    rel="stylesheet"
  />
</head>

Or via an @import statement

<head>
  <style>
    @import url('https://fonts.googleapis.com/css2?family=Readex+Pro:wght@200;300;400;500;600;700&family=Roboto&display=swap');
  </style>
</head>
  1. Your main stylesheet loads fonts
/* main.css */
@font-face {
  font-family: 'Fira Sans';
  src: url('fonts/fira/eot/FiraSans-Regular.eot');
  src:
    url('fonts/fira/eot/FiraSans-Regular.eot') format('embedded-opentype'),
    url('fonts/fira/woff2/FiraSans-Regular.woff2') format('woff2'),
    url('fonts/fira/woff/FiraSans-Regular.woff') format('woff'),
    url('fonts/fira/woff2/FiraSans-Regular.ttf') format('truetype');
  font-weight: normal;
  font-style: normal;
}

Icon Fonts: None of my icons are rendering​

Theme Providers: My components don't look right/compile because they can't access providers​

Theme Provider or other application-level wrappers like I18n or Material UI work by injecting themselves around your application. When you're component testing, you haven't rendered the component hierarchy surrounding your component.

To solve issues like these, people review the Custom Commands and Wrappers

To first explain why it's not right, you first have to explain what production-like even means.

So we have this before & after up, and now our job is to step through the component under test and try to figure out where the differences between Production and Test are.

Sometimes these are as simple as colors or fonts not lining up. Other times, the entire component or sections of it may not compile.

The reason this doesn't look right is because:

  1. My browser supports dark mode
  2. The <App> component provides its own styles

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