How to Write a Playwright Test to Ensure a Single Server Call

JavaScript Playwright: Ensuring a Single Server Call in Tests

In the world of web automation testing, ensuring that an action triggers a specific number of server calls is a crucial part of verifying application stability. A common problem developers face is actions resulting in infinite server calls due to bugs in the code. In this tutorial, we will discuss how to write a test using Playwright to ensure that an action makes exactly one server call.

Why Is This Test Important?

Infinite server calls can significantly impact application performance, increase server load, and degrade user experience. Using Playwright, a popular testing framework, you can effectively monitor network requests and ensure that your application only sends the necessary number of server calls.

Prerequisites

• Basic knowledge of JavaScript and Node.js.
• Playwright installed in your project. You can install it using:

  npm install playwright

Step 1: Setting Up Playwright

Before writing the test, make sure you have Playwright installed. Create a new test.js file and set up the browser context:

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

test('should trigger only one server call', async ({ page }) => {
    await page.goto('https://your-website.com');
});
    

Step 2: Monitoring Network Requests

To monitor network requests, you can use Playwright's page.on('request') event. We will filter out the specific server request we are interested in:

// Variable to count the number of requests
let requestCount = 0;

page.on('request', (request) => {
    if (request.url().includes('/api/target-endpoint')) {
        requestCount++;
    }
});
    

Step 3: Writing the Test Logic

Now, let's complete the test to ensure that the action on your webpage triggers only one server call:

test('should trigger only one server call', async ({ page }) => {
    let requestCount = 0;
    
    // Monitor requests to the specific endpoint
    page.on('request', (request) => {
        if (request.url().includes('/api/target-endpoint')) {
            requestCount++;
        }
    });

    await page.goto('https://your-website.com');
    
    // Perform the action that triggers the server call
    await page.click('#trigger-button');
    
    // Wait for any pending network activities to finish
    await page.waitForTimeout(2000);
    
    // Assert that only one request was made
    expect(requestCount).toBe(1);
});
    

Step 4: Running the Test

To execute the test, use the following command in your terminal:

npx playwright test test.js

This will run the test and confirm if the action triggers a single server call.

Conclusion

By using Playwright to monitor network requests, you can prevent unnecessary server calls and optimize your web application's performance. This method is especially useful for avoiding issues like infinite loops caused by erroneous server calls. Implementing tests like this ensures that your application behaves as expected, improving both performance and user experience.

Further Reading

• Playwright Test API Documentation
• JavaScript Guide - MDN
• Node.js Documentation

Frequently Asked Questions (FAQs)

1. Why does my action trigger multiple server calls?

This could be due to event listeners being attached multiple times or loops within your code that unintentionally trigger the action repeatedly.

2. Can I use this approach for other testing frameworks?

Yes, while this example uses Playwright, similar logic can be applied to other frameworks like Selenium or Cypress using their respective network request monitoring features.