Add testing

[jackdomleo7]

It would be useful to add some kind of automated testing so developers using this package are assured. And so we have confidence when publishing a new version.

Some investigation is first needed into the best tool. Below are some requirements needed:

• Tests must run quickly (Cypress is good but can often be very heavy to install and run and can take a while)
• Must test the visuals, I.e. take a screenshot and compare
• Run tests in pipeline