Do you know any tools for load testing web applications?
Checkout loader.io for free online load testing.
If you're looking for something opensource that you can run from your CLI then you might like https://artillery.io/
You might also like Hey - https://github.com/rakyll/hey which is written in go and is really simple to use
Or Wrk - https://github.com/wg/wrk which is the industry standard and successor of Apache Benchmark - https://httpd.apache.org/docs/2.4/programs/ab.html
I'd personally recommend Hey. It's easy to use and produces a neat report.
It depends on your stack and what kind of testing you want to have. Unit and integration tests are coupled to the language you use. For system tests (end-to-end) I would recommend Cypress.io: https://www.cypress.io/. It's a pleasure to use!
Thanks for the answers. I will try hey, and loader.io.
About the testing i need is just load testing. I work with rails and already use unit and integration testing.