The Complete Guide to Visual Testing

Visual testing catches bugs that functional tests miss. Here's everything you need to know.

What is Visual Testing?

Visual testing compares screenshots of your application against known-good baselines. It catches:

CSS regressions

Layout shifts

Font rendering issues

Color changes

Responsive design bugs

Why Visual Testing Matters

Functional tests verify behavior: "Does clicking the button submit the form?" Visual tests verify appearance: "Does the button look correct?"

Consider this scenario:

Your button still works (functional test passes)

But someone changed its color to white on a white background

Users can't see the button anymore

Visual test would catch this

Types of Visual Testing

1. Pixel-by-Pixel Comparison

Compares every pixel between baseline and new screenshot. Very accurate but sensitive to anti-aliasing and minor rendering differences.

2. DOM-Based Comparison

Compares the structure and computed styles of elements. Less sensitive to rendering variations but may miss some visual bugs.

3. AI-Powered Comparison

Uses machine learning to identify meaningful visual changes while ignoring noise. This is what Qovr uses.

Implementing Visual Testing

Step 1: Capture Baselines

Run your test suite and approve the initial screenshots as baselines.

Step 2: Run Comparisons

On each test run, compare new screenshots against baselines.

Step 3: Review Changes

When differences are detected, review them:

If intentional: Update the baseline

If unintentional: Fix the bug

Step 4: Handle Dynamic Content

Mask or ignore areas with dynamic content (timestamps, user avatars, etc.).

Best Practices

Test at multiple viewport sizes - Responsive bugs are common

Use consistent test data - Dynamic content causes false positives

Test loading states - Capture spinners and skeletons too

Version your baselines - Keep them in source control

Getting Started with Qovr

Qovr makes visual testing simple:

Enable "Visual Assertions" in project settings

Run your tests to capture baselines

Future runs automatically compare against baselines

Review changes in the dashboard

Visual testing is the safety net your functional tests don't provide. Start today.