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Lighthouse Service

A WebdriverIO service that allows you to run accessibility and performance tests with Google Lighthouse.

Note: this service currently only supports tests running on Google Chrome or Chromium! Given that most cloud vendors don't expose access to the Chrome DevTools Protocol this service also usually only works when running tests locally or through a Selenium Grid v4 or higher.

Installation​

The easiest way is to keep @wdio/lighthouse-service as a dev dependency in your package.json, via:

npm install @wdio/lighthouse-service --save-dev

Instructions on how to install WebdriverIO can be found here.

Configuration​

In order to use the service you just need to add the service to your service list in your wdio.conf.js, like:

// wdio.conf.js
export const config = {
    // ...
    services: ['devtools'],
    // ...
};

Usage​

The @wdio/lighthouse-service allows you to run Google Lighthouse accessibility and performance tests through WebdriverIO.

Performance Testing​

The Lighthouse service allows you to capture performance data from every page load or page transition that was caused by a click. To enable it call browser.enablePerformanceAudits(<options>). After you are done capturing all necessary performance data disable it to revert the throttling settings, e.g.:

import assert from 'node:assert'

describe('JSON.org page', () => {
    before(async () => {
        await browser.enablePerformanceAudits()
    })

    it('should load within performance budget', async () => {
        /**
         * this page load will take a bit longer as the DevTools service will
         * capture all metrics in the background
         */
        await browser.url('http://json.org')

        let metrics = await browser.getMetrics()
        assert.ok(metrics.speedIndex < 1500) // check that speedIndex is below 1.5ms

        let score = await browser.getPerformanceScore() // get Lighthouse Performance score
        assert.ok(score >= .99) // Lighthouse Performance score is at 99% or higher

        $('=Esperanto').click()

        metrics = await browser.getMetrics()
        assert.ok(metrics.speedIndex < 1500)
        score = await browser.getPerformanceScore()
        assert.ok(score >= .99)
    })

    after(async () => {
        await browser.disablePerformanceAudits()
    })
})

You can emulate a mobile device by using the emulateDevice command, throttling CPU and network as well as setting mobile as form factor:

await browser.emulateDevice('iPhone X')
await browser.enablePerformanceAudits({
    networkThrottling: 'Good 3G',
    cpuThrottling: 4,
    formFactor: 'mobile'
})

The following commands with their results are available:

getMetrics​

Gets the most commonly used performance metrics, e.g.:

console.log(await browser.getMetrics())
/**
 * { timeToFirstByte: 566,
 *   serverResponseTime: 566,
 *   domContentLoaded: 3397,
 *   firstVisualChange: 2610,
 *   firstPaint: 2822,
 *   firstContentfulPaint: 2822,
 *   firstMeaningfulPaint: 2822,
 *   largestContentfulPaint: 2822,
 *   lastVisualChange: 15572,
 *   interactive: 6135,
 *   load: 8429,
 *   speedIndex: 3259,
 *   totalBlockingTime: 31,
 *   maxPotentialFID: 161,
 *   cumulativeLayoutShift: 2822 }
 */

getDiagnostics​

Get some useful diagnostics about the page load.

console.log(await browser.getDiagnostics())
/**
 * { numRequests: 8,
 *   numScripts: 0,
 *   numStylesheets: 0,
 *   numFonts: 0,
 *   numTasks: 237,
 *   numTasksOver10ms: 5,
 *   numTasksOver25ms: 2,
 *   numTasksOver50ms: 2,
 *   numTasksOver100ms: 0,
 *   numTasksOver500ms: 0,
 *   rtt: 147.20600000000002,
 *   throughput: 47729.68474448835,
 *   maxRtt: 176.085,
 *   maxServerLatency: 1016.813,
 *   totalByteWeight: 62929,
 *   totalTaskTime: 254.07899999999978,
 *   mainDocumentTransferSize: 8023 }
 */

getMainThreadWorkBreakdown​

Returns a list with a breakdown of all main thread tasks and their total duration.

console.log(await browser.getMainThreadWorkBreakdown())
/**
 * [ { group: 'styleLayout', duration: 130.59099999999998 },
 *   { group: 'other', duration: 44.819 },
 *   { group: 'paintCompositeRender', duration: 13.732000000000005 },
 *   { group: 'parseHTML', duration: 3.9080000000000004 },
 *   { group: 'scriptEvaluation', duration: 2.437999999999999 },
 *   { group: 'scriptParseCompile', duration: 0.20800000000000002 } ]
 */

getPerformanceScore​

Returns the Lighthouse Performance Score which is a weighted mean of the following metrics: firstContentfulPaint, speedIndex, largestContentfulPaint, cumulativeLayoutShift, totalBlockingTime, interactive, maxPotentialFID or cumulativeLayoutShift.

console.log(await browser.getPerformanceScore())
/**
 * 0.897826278457836
 */

enablePerformanceAudits​

Enables auto performance audits for all page loads that are caused by calling the url command or clicking on a link or anything that causes a page load. You can pass in a config object to determine some throttling options. The default throttling profile is Good 3G network with a 4x CPU throttling.

await browser.enablePerformanceAudits({
    networkThrottling: 'Good 3G',
    cpuThrottling: 4,
    cacheEnabled: true,
    formFactor: 'mobile'
})

The following network throttling profiles are available: offline, GPRS, Regular 2G, Good 2G, Regular 3G, Good 3G, Regular 4G, DSL, Wifi and online (no throttling).

PWA Testing​

With the checkPWA command, you can validate if your web app is compliant to the latest web standards when it comes to progressive web apps. It checks:

  • whether your app is installable
  • provides a service worker
  • has a splash screen
  • provides Apple Touch and Maskable Icons
  • can be served on mobile devices

If you are not interested in one of these checks you can pass in a list of checks you like to run. The passed property will return true if all checks pass. If they fail you can use the details property to enrich your failure message with details of the failure.

// open page first
await browser.url('https://webdriver.io')
// validate PWA
const result = await browser.checkPWA()
expect(result.passed).toBe(true)

startTracing(categories, samplingFrequency) Command​

Start tracing the browser. You can optionally pass in custom tracing categories (defaults to this list) and the sampling frequency (defaults to 10000).

await browser.startTracing()

endTracing Command​

Stop tracing the browser.

await browser.endTracing()

getTraceLogs Command​

Returns the trace-logs that were captured within the tracing period. You can use this command to store the trace logs on the file system to analyse the trace via Chrome DevTools interface.

import fs from 'node:fs/promises'

await browser.startTracing()
await browser.url('http://json.org')
await browser.endTracing()

await fs.writeFile('/path/to/tracelog.json', JSON.stringify(browser.getTraceLogs()))

getPageWeight Command​

Returns page weight information of the last page load.

await browser.startTracing()
await browser.url('https://webdriver.io')
await browser.endTracing()

console.log(await browser.getPageWeight())
// outputs:
// { pageWeight: 2438485,
//   transferred: 1139136,
//   requestCount: 72,
//   details: {
//       Document: { size: 221705, encoded: 85386, count: 11 },
//       Stylesheet: { size: 52712, encoded: 50130, count: 2 },
//       Image: { size: 495023, encoded: 482433, count: 36 },
//       Script: { size: 1073597, encoded: 322854, count: 15 },
//       Font: { size: 84412, encoded: 84412, count: 5 },
//       Other: { size: 1790, encoded: 1790, count: 2 },
//       XHR: { size: 509246, encoded: 112131, count: 1 } }
// }

For more information on WebdriverIO see the homepage.

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