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Experimental: components

Playwright Test can now test your components.

Example

Here is what a typical component test looks like:

test('event should work', async ({ mount }) => {
let clicked = false;

// Mount a component. Returns locator pointing to the component.
const component = await mount(<Button title="Submit"
onClick={() => clicked = true}>
</Button>);

// As with any Playwright test, assert locator text.
await expect(component).toContainText('Submit');

// Perform locator click. This will trigger the event.
await component.click();

// Assert that respective events have been fired.
expect(clicked).toBeTruthy();
});

How to get started

Adding Playwright Test to an existing React, Vue, Svelte or Solid project is easy. Below are the steps to enable Playwright Test for a sample create-react-app with TypeScript template.

Step 1: Install Playwright Test for components for your respective framework

npm init playwright@latest -- --ct

This step creates several files in your workspace:

playwright/index.html

This file defines an html file that will be used to render components during testing. It must contain element with id="root", that's where components are mounted. It must also link the script called playwright/index.[tj]s.

<html lang="en">
<body>
<div id="root"></div>
<script type="module" src="./index.ts"></script>
</body>
</html>

playwright/index.ts

You can include stylesheets, apply theme and inject code into the page where component is mounted using this script. It can be either a .js or .ts file.

// Apply theme here, add anything your component needs at runtime here.

Step 2. Create a test file src/App.spec.{ts,tsx}

import { test, expect } from '@playwright/experimental-ct-react';
import App from './App';

test.use({ viewport: { width: 500, height: 500 } });

test('should work', async ({ mount }) => {
const component = await mount(<App />);
await expect(component).toContainText('Learn React');
});

Step 3. Run the tests

You can run tests using the VS Code extension or the command line.

npm run test-ct

Further reading: configure reporting, browsers, tracing

Refer to Playwright config for configuring your project.

Hooks

You can use beforeMount and afterMount hooks to configure your app. This lets you setup things like your app router, fake server etc. giving you the flexibility you need. You can also pass custom configuration from the mount call from a test, which is accessible from the hooksConfig fixture.

playwright/index.ts

This includes any config that needs to be run before/after mounting the component. Here's an example of how to setup miragejs mocking library:

import { beforeMount } from '@playwright/experimental-ct-react/hooks';
import { createServer } from "miragejs"

beforeMount(async ({ hooksConfig }) => {
// Setting default values if custom config is not provided
const users = hooksConfig.users ?? [
{ id: "1", name: "Luke" },
{ id: "2", name: "Leia" },
{ id: "3", name: "Han" },
];
createServer({
routes() {
this.get("/api/users", () => users)
},
});
});

In your test file:

// src/Users.spec.tsx
import { test, expect } from "@playwright/experimental-ct-react";
import React from "react";
import { Users } from "./Users";

test("should work", async ({ mount }) => {
const component = await mount(<Users />, {
hooksConfig: {
users: [
{ id: "4", name: "Anakin" },
{ id: "5", name: "Padme" },
]
}
});
await expect(component.locator("li")).toContainText([
"Anakin",
"Padme",
]);
});

Under the hood

When Playwright Test is used to test web components, tests run in Node.js, while components run in the real browser. This brings together the best of both worlds: components run in the real browser environment, real clicks are triggered, real layout is executed, visual regression is possible. At the same time, test can use all the powers of Node.js as well as all the Playwright Test features. As a result, the same parallel, parametrized tests with the same post-mortem Tracing story are available during component testing.

Here is how this is achieved:

  • Once the tests are executed, Playwright creates a list of components that the tests need.
  • It then compiles a bundle that includes these components and serves it using a local static web server.
  • Upon the mount call within the test, Playwright navigates to the facade page /playwright/index.html of this bundle and tells it to render the component.
  • Events are marshalled back to the Node.js environment to allow verification.

Playwright is using Vite to create the components bundle and serve it.

Known issues and limitations

Q) I can't import anything other than the components from TSX/JSX/Component files

As per above, you can only import your components from your test file. If you have utility methods or constants in your TSX files, it is advised to extract them into the TS files and import those utility methods and constants from your component files and from your test files. That allows us to not load any of the component code in the Node-based test runner and keep Playwright fast at executing your tests.

Q) I have a project that already uses Vite. Can I reuse the config?

At this point, Playwright is bundler-agnostic, so it is not reusing your existing Vite config. Your config might have a lot of things we won't be able to reuse. So for now, you would copy your path mappings and other high level settings into the ctViteConfig property of Playwright config.

import { defineConfig } from '@playwright/experimental-ct-react';

export default defineConfig({
use: {
ctViteConfig: { ... },
},
});

Q) What's the difference between @playwright/test and @playwright/experimental-ct-{react,svelte,vue,solid}?

test('…', async { mount, page, context } => {
// …
});

@playwright/experimental-ct-{react,svelte,vue,solid} wrap @playwright/test to provide an additional built-in component-testing specific fixture called mount:

import { test, expect } from '@playwright/experimental-ct-react'
import HelloWorld from './HelloWorld'

test.use({ viewport: { width: 500, height: 500 } })

test('should work', async ({ mount }) => {
const component = await mount(<HelloWorld msg="greetings" />);
await expect(component).toContainText('Greetings')
})

Additionally, it adds some config options you can use in your playwright-ct.config.{ts,js}.

Finally, under the hood, each test re-uses the context and page fixture as a speed optimization for Component Testing. It resets them in between each test so it should be functionally equivalent to @playwright/test's guarantee that you get a new, isolated context and page fixture per-test.

Q) Can I use @playwright/test and @playwright/experimental-ct-{react,svelte,vue,solid}?

Yes. Use a Playwright Config for each and follow their respective guides (E2E Playwright Test, Component Tests)

Q) Why can't I pass a variable to mount?

This is a known issue. The following pattern does not work:

const app = <App />;
await mount(app);

results in

undefined: TypeError: Cannot read properties of undefined (reading 'map')

while this works:

await mount(<App />);

Q) How can I use Vite plugins?

You can specify plugins via Vite config for testing settings. Note that once you start specifying plugins, you are responsible for specifying the framework plugin as well, vue() in this case:

import { defineConfig, devices } from '@playwright/experimental-ct-vue'

import { resolve } from 'path'
import vue from '@vitejs/plugin-vue'
import AutoImport from 'unplugin-auto-import/vite'
import Components from 'unplugin-vue-components/vite'

export default defineConfig({
testDir: './tests/component',
use: {
trace: 'on-first-retry',
ctViteConfig: {
plugins: [
vue(),
AutoImport({
imports: [
'vue',
'vue-router',
'@vueuse/head',
'pinia',
{
'@/store': ['useStore'],
},
],
dts: 'src/auto-imports.d.ts',
eslintrc: {
enabled: true,
},
}),
Components({
dirs: ['src/components'],
extensions: ['vue'],
}),
],
resolve: {
alias: {
'@': resolve(__dirname, './src'),
},
},
},
}
});

don't forget to initialize your plugins, for example if you are using Pinia, add init code into your playwright/index.js:

import { createTestingPinia } from '@pinia/testing';

createTestingPinia({
createSpy: (args) => {
console.log('spy', args)
return () => {
console.log('spyreturns')
}
},
});