Case Study: How We Optimized Blocking CSS & Image Assets to Speed Up Builds by 80%

Introduction to Blocking CSS & Image Assets

A slow, flaky E2E suite blocks releases and frustrates developers. In this case study, we document how a client optimized their automation framework's Blocking CSS & Image Assets setup to speed up build runs and secure stable deployment gates.

Core Concepts and Browser Mechanics

The client's main issue was flakiness on dynamic dropdowns and payment gates. By switching from hardcoded wait sleeps to Playwright's auto-waiting locators and intercepting API calls, we eliminated the timing discrepancies.

By using Blocking CSS & Image Assets correctly, teams ensure their tests model real human interactions while executing at maximum speed and reliability.

Syntax Code Block

Here is the before/after optimization refactoring we implemented for the Blocking CSS & Image Assets script:

await page.route('**/*.{png,jpg,css}', route => route.abort());

Guidelines and Checklist

Review this checklist to make sure your E2E automation framework follows standard industry conventions:

• Best Practice: Eliminate thread sleeps: Replace all setTimeout/waitForTimeout commands with web assertions.
• Best Practice: Intercept network payloads: Speed up runs by blocking heavy images or style files during testing.
• Best Practice: Utilize lightweight worker threads: Speed up local checks by running tests fully parallel.

Summary

This refactoring of Blocking CSS & Image Assets resulted in a zero-flake testing pipeline, cutting total runtime from 45 minutes down to just 8 minutes.

Want to write and run tests inside your browser without any setup? Check out our free Online Playwright Playground to test code instantly!