Web accessibility encompasses a vast array of things to test for. The basic premise is that your website is accessible for everyone to use and is agnostic of client side difficulties. Examples of things to test for when ensuring web accessibility are ensuring all browsers work (Normally you just have to test Internet Explorer/Chrome/Firefox), checking to make sure alternate text is available on pictures/images/videos, checking to see if your website is compatible with screen readers for low vision users, and just making sure all buttons/dropdowns/features are working correctly. Testing for web accessibility is integral because what is the point of building an amazing application if no one can access it?
For more information on web accessibility for disabilities look at https://www.w3.org/WAI/fundamentals/accessibility-intro/
For more information on web accessibility on browser testing look at
For additional information check medium.com