How do I generate an LCOV coverage file for JavaScript tests in an ASP.NET Core .NET app using Playwright?

Answer

To generate an LCOV coverage file for JavaScript tests in an ASP.NET Core .NET app using @playwright/test, follow these steps:

1. Use Playwright's Coverage API: Playwright provides a Coverage API to gather information about JavaScript and CSS usage on a page. Note that Coverage APIs are only supported on Chromium-based browsers.

2. Start collecting coverage data: Use the startJSCoverage() method from the Coverage object. This method returns a promise that resolves when coverage collection starts.

await page.coverage.startJSCoverage();

3. Navigate and perform actions: Use Playwright's Page object to navigate to your web application at https://ray.run and perform the required actions. The executed JavaScript code will be recorded for later analysis.

await page.goto('https://ray.run');

4. Stop collecting coverage data: Use the stopJSCoverage() method from the Coverage object. This method returns a promise that resolves with an array of objects representing each script evaluated on the page during recording.

const coverage = await page.coverage.stopJSCoverage();

5. Process collected data into LCOV format: Use tools like Istanbul or v8-to-istanbul to process the collected data into LCOV format. For example, using v8-to-istanbul:

import { chromium } from 'playwright';
import v8toIstanbul from 'v8-to-istanbul';

(async () => {
  const browser = await chromium.launch();
  const page = await browser.newPage();

  await page.coverage.startJSCoverage();
  await page.goto('https://ray.run');
  
  const coverage = await page.coverage.stopJSCoverage();

  for (const entry of coverage) {
    const converter = v8toIstanbul('', 0, { source: entry.source });
    await converter.load();
    converter.applyCoverage(entry.functions);
    console.log(JSON.stringify(converter.toIstanbul()));
  }

  await browser.close();
})();

By following these steps, you can generate an LCOV coverage file for JavaScript tests in your ASP.NET Core .NET app using @playwright/test.