The only previous post about using Selenium with Eikon I could find was this one.
https://community.developers.refinitiv.com/questions/37754/python-selenium-authentication-error.html
This post is not about automated testing and the response is not relevant to your question. This said App Studio was not designed with automated testing in mind. While we have no objections against using Selenium or any other framework for the purpose of automated testing, there are several technical challenges that would need to be solved. One such challenge is user access control. User authorization relying on App Studio Authorization Service can only work when the app is instantiated in Eikon. For automated testing purposes you'd need to bypass user authorization relying on App Studio Authorization Service. Once you've solved user access control challenge you should be able to run automated unit tests. However since JET library can only be used in Eikon, unit tests for any functionality that relies on JET will fail. If your app is available on Eikon Web you may be able to do automated testing including functionality that relies on JET against your app in Eikon Web. I don't believe anyone has done this before, hence I'm not sure it will work. But it may be worth a try.