Boost your Playwright suite with Lighthouse integration

Boost your Playwright suite with Lighthouse integration

Table of Contents:

1. Introduction
2. Installing the Lighthouse npm Package
3. Creating a custom fixture for Lighthouse
4. Using the custom fixture in Playwright Suite
5. Creating a custom expect method for Lighthouse
6. Integrating the custom method with TypeScript
7. Usage of the Lighthouse fixture
8. Checking the result in the terminal
9. Running Lighthouse in UI mode
10. Running Lighthouse in production mode

Article: Integrating Lighthouse in Your Playwright Suite

Introduction:

In this article, we will explore how to integrate Lighthouse into your Playwright suite. Lighthouse is an open-source tool from Google that helps in auditing the performance, accessibility, and best practices of web applications. By using Lighthouse, you can gain insights into your application's performance and identify areas for improvement. We will cover the installation process, creating custom fixtures, using the fixtures in Playwright Suite, creating a custom expect method, integrating it with TypeScript, and taking AdVantage of Lighthouse's features for auditing the performance of your web application.

Installing the Lighthouse npm package:

To begin, You need to install the Lighthouse npm package. Open your terminal and run the following command:

npm install lighthouse

This will install the Lighthouse package in your project.

Creating a custom fixture for Lighthouse:

Next, we will Create a custom fixture for Lighthouse that can be used in your Playwright Suite. The custom fixture will allow you to define the categories and thresholds for the audit. Here's an example of how you can create a custom fixture:

const { lighthouse, defaultThresholds } = require('lighthouse');

const customFixture = async (page, options) => {
  const customThresholds = {
    performance: 0.9,
    accessibility: 0.9,
    bestPractices: 0.9,
    seo: 0.9,
    pwa: 0.9,
  };

  // Check if custom thresholds are provided
  if (options && options.thresholds) {
    Object.assign(customThresholds, options.thresholds);
  }

  const { lhr } = await lighthouse(page.url(), { logLevel: 'info' });

  const result = Object.entries(lhr.categories).reduce((accumulator, [category, { score }]) => {
    if (customThresholds[category]) {
      if (score >= customThresholds[category]) {
        accumulator[category] = score;
      } else {
        accumulator[category] = null;
      }
    }
    return accumulator;
  }, {});

  return result;
};

Using the custom fixture in Playwright Suite:

To use the custom fixture in your Playwright Suite, you can create a test and use the customFixture function we defined earlier. Here's an example:

const { test, expect } = require('@playwright/test');

test('Check page performance', async ({ page, browserName, playwright }) => {
  if (browserName !== 'chromium') {
    // Lighthouse only works with Chromium
    return;
  }

  const browser = await playwright.chromium.launch({
    args: ['--remote-debugging-port=9222'],
  });

  const lighthouseResult = await customFixture(page, {
    thresholds: {
      performance: 0.9,
      accessibility: 0.9,
      bestPractices: 0.9,
      seo: 0.9,
      pwa: 0.9,
    },
  });

  expect(lighthouseResult).toBeAllThresholdsMatched();
});

Creating a custom expect method for Lighthouse:

To create a custom expect method for Lighthouse, we can extend the expect object provided by Playwright. This method will compare the received thresholds with the expected thresholds and return the result. Here's an example implementation:

const lighthouseMatchers = (received) => ({
  toMatchThreshold(expected) {
    const differences = {};

    for (const [category, threshold] of Object.entries(expected)) {
      if (received[category] < threshold) {
        differences[category] = threshold - received[category];
      }
    }

    if (Object.keys(differences).length === 0) {
      return {
        message: () => `Expected thresholds matched`,
        pass: true,
      };
    } else {
      return {
        message: () => `Expected thresholds not matched. Differences: ${JSON.stringify(differences)}`,
        pass: false,
      };
    }
  },
});

expect.extend(lighthouseMatchers);

Integrating the custom method with TypeScript:

If you are working with TypeScript, you need to integrate the custom expect method into the type system. To do this, declare the MatcherRnt interface in the global namespace and add the toMatchThreshold method to it. Here's how you can achieve this:

declare global {
  namespace PlaywrightTest {
    interface Matchers<R> {
      toMatchThreshold: (expected: LighthouseThresholds) => R;
    }
  }
}

interface LighthouseThresholds {
  performance: number;
  accessibility: number;
  bestPractices: number;
  seo: number;
  pwa: number;
}

Usage of the Lighthouse fixture:

To use the Lighthouse fixture, simply call it with the page object and the desired thresholds. Here's an example:

const lighthouseResult = await customFixture(page, {
  thresholds: {
    performance: 0.9,
    accessibility: 0.9,
    bestPractices: 0.9,
    seo: 0.9,
    pwa: 0.9,
  },
});

Checking the result in the terminal:

To check the result of the Lighthouse audit, you can use the Playwright UI mode. Simply run the command playwright test --ui in your terminal, and a new window will open. In the Lighthouse section, you can run the tests and view the results.

Running Lighthouse in UI mode:

To run Lighthouse in UI mode, you can use the command playwright test --ui. This opens a new window where you can Interact with the Lighthouse tool and run tests on your web application.

Running Lighthouse in production mode:

To run Lighthouse in production mode, you can use the command playwright test --production. This script will build your application in production mode and then run the Lighthouse test. This ensures that all the bundles are optimized for a real production environment.

In conclusion, integrating Lighthouse into your Playwright suite allows you to perform comprehensive audits of your web application's performance, accessibility, and best practices. By creating custom fixtures and expect methods, you can tailor the audits to your specific requirements and thresholds. Make sure to run the Lighthouse audit in both development and production modes to ensure optimal performance in real-world scenarios.

Highlights:

• Integrate Lighthouse into your Playwright suite
• Audit performance, accessibility, and best practices
• Create custom fixtures and expect methods
• Use Lighthouse in development and production modes

FAQ:

Q: Can I use Lighthouse with browsers other than Chromium? A: No, Lighthouse currently only works with Chromium.

Q: How do I define custom thresholds for the Lighthouse audit? A: You can pass the desired thresholds as options when calling the Lighthouse fixture.

Q: Does Lighthouse support TypeScript? A: Yes, you can integrate the custom expect method with TypeScript by adding the necessary declarations.

Q: How can I check the results of the Lighthouse audit? A: You can use the Playwright UI mode to run the tests and view the results.

Q: Is it necessary to run the Lighthouse audit in both development and production modes? A: Yes, running the audit in both modes allows you to identify performance issues specific to each environment.