Playwright Inspector

Detailed explanation

The Playwright Inspector is a powerful debugging tool that ships with the Playwright framework. It provides a visual interface to inspect the state of your web application during test execution, making it significantly easier to identify and resolve issues. Unlike traditional browser developer tools, the Playwright Inspector is specifically designed to work seamlessly with Playwright's automation capabilities. It allows you to step through your tests line by line, observe the DOM at each step, generate reliable selectors, and analyze network traffic. This integrated approach streamlines the debugging process and improves the overall efficiency of your testing workflow.

One of the primary benefits of the Playwright Inspector is its ability to generate selectors automatically. When writing end-to-end tests, identifying the correct element to interact with can be challenging. The Inspector allows you to visually select an element in the browser, and it will generate a recommended Playwright selector for that element. This feature significantly reduces the time and effort required to create robust and maintainable tests. The generated selectors are often more resilient to changes in the application's UI compared to manually crafted CSS selectors or XPath expressions.

To launch the Playwright Inspector, you typically run your Playwright tests with the --debug flag or set the headless option to false in your Playwright configuration. For example:

npx playwright test --debug

or in your playwright.config.js:

module.exports = {
  use: {
    headless: false,
  },
};

When the Inspector launches, it opens a separate window alongside your browser instance. This window provides a control panel with several key features:

• Step-by-step execution: You can step through your test code line by line, observing the state of the application at each step. This is invaluable for understanding the exact sequence of events that lead to a failure.
• DOM inspection: The Inspector allows you to inspect the DOM of the page at any point during the test execution. You can view the HTML structure, CSS styles, and attributes of elements, helping you understand how the application is rendered.
• Selector generation: As mentioned earlier, the Inspector can automatically generate Playwright selectors for elements you select in the browser. This feature significantly simplifies the process of creating reliable tests.
• Network analysis: The Inspector provides a network panel that allows you to monitor the HTTP requests and responses made by the application during the test execution. This can be helpful for identifying performance bottlenecks or issues with API calls.
• Console output: The Inspector displays the console output from your test code, including any error messages or log statements. This can provide valuable clues about the cause of failures.

Here's a simple example of how you might use the Playwright Inspector to debug a test:

const { test, expect } = require('@playwright/test');
 
test('example test', async ({ page }) => {
  await page.goto('https://example.com');
  await page.getByRole('link', { name: 'More information...' }).click(); // Intentionally incorrect selector
  await expect(page).toHaveURL(/example.com/);
});

If you run this test with the --debug flag, the Playwright Inspector will launch when the test fails. You can then use the Inspector to:

1. Step through the test code to see exactly where the failure occurs.
2. Inspect the DOM to understand why the selector page.getByRole('link', { name: 'More information...' }) is not working. Perhaps the link text is slightly different.
3. Use the Inspector's selector generation tool to create a correct selector for the link.
4. Modify the test code with the correct selector and re-run the test.

Best practices for using the Playwright Inspector include:

• Start debugging early: Don't wait until you have a complex test suite to start using the Inspector. Use it from the beginning to understand how your tests interact with the application.
• Use the step-by-step execution feature: This is the most powerful way to understand the sequence of events that lead to a failure.
• Leverage the selector generation tool: This can save you a significant amount of time and effort when creating tests.
• Inspect the DOM frequently: Understanding the DOM structure is crucial for writing robust tests.
• Analyze network traffic: This can help you identify performance bottlenecks or issues with API calls.
• Combine with trace viewer: For more complex scenarios, the Playwright trace viewer provides a more detailed record of the test execution, including screenshots, network requests, and console logs. The Inspector can be used in conjunction with the trace viewer to provide a comprehensive debugging experience.

In summary, the Playwright Inspector is an indispensable tool for debugging and creating Playwright tests. Its visual interface, step-by-step execution, selector generation, and network analysis capabilities significantly streamline the testing process and improve the quality of your tests. By following best practices and leveraging the Inspector's features, you can efficiently identify and resolve issues, create robust tests, and ensure the reliability of your web applications.

Further reading

• Playwright Debugging Tools
• Playwright Inspector Documentation
• Playwright Selectors