At regex 101, you will no longer have problems of figuring out how they work or test how it works.
I have come across this little beauty https://regex101.com/ .
All you have to do is, have a copy of the text you are going to search and paste it on the “TEST STRING” text box, then start typing your regex above and see the results live.
This website has a number of tools to help you use regular expressions like a pro.
You can also write tests (under “unit tests”) where you type conditions when it should and should not pass, so you can have a better confidence at the regex you are working with. You may decide to save that regex, copy the URL somewhere safe and you can revisit that same expression as you had left of.
Simply amazing, the user interface and user friendliness of this website is all too well done and it’s all free.