Let's say we have a chat software that can be used via:
- a mobile application
- standalone app
- web application
A User using one of this platform can use the software to communicate with another User in another platform.
When we talk about End to end scenario, shall we create automatic UI test so that we make sure that every User with every device can communicate with every other User with other devices? Shall we also cover the case that the system is working well using a big number of Users?
I believe that the E2E test, in this case should cover only the bare minimum communication among the three devices, no more than that, given the reliability and the speed of the test, and I would delegate the health check of the connection between the services to some monitoring tool, so that in case of a failure we are able to detect immediately if the system can work or not.