When you start in white hat pen-testing journey
you might get confused with where to start how to do what i can do

basically there is no story board to tell what you should do and what is become first so lets skip this and get to the point

a plugin called Xss Validator for Burp Suite made Xss easy to test

its a powerful plug-in that will help you out to find Xss Vulns

What we need

1 - Burp Suite
2 - Apache

How to Use   Xss Validator

1 - Download The Plug-in From here
2 - download phantomjs

For Ubuntu users use

$ sudo apt-get install phantomjs

3 - download the files from GitHub from here

4 - move to /path/extractedFiles/xss-detector

5 - lunch the xss.js with phantomjs
phantomjs xss.js

now you are ready to go

open Burp Suite and load the Plug-in from Extender

as follow