Some of the Regular Expression(regex) test websites of reference
Online Regex tester and visualizer - Python, PHP, Ruby, JavaScript, Java
Online regular expression tester for Python, PHP, Ruby, JS, Java and MySQL. Regex visualizer. Syntax highlighting. Cheatsheet. Generate string corresponding to a regex.
Regex Storm - Online Resource for .NET Regular Expressions
Online tool for building and testing .NET regular expressions. Features a .NET regex tester and complete .NET regex reference.
RegExr: Learn, Build, & Test RegEx
RegExr is an online tool to learn, build, & test Regular Expressions (RegEx / RegExp).
regex101: build, test, and debug regex
Regular expression tester with syntax highlighting, explanation, cheat sheet for PHP/PCRE, Python, GO, JavaScript, Java. Features a regex quiz & library.