What are the best web functional testing framework available?

I'm looking for a framework or a set of tools that can help testing for one or more web apps that i'm working on. The front end side is written in node/react if that helps. I'm looking for something that - Ideally integrates well with continuos CI (i'm using Travis) - It's lightweight - Allows testing of 'flows' , not just a single page - As cross browser and cross device as possible

What are you guys using?