How to do end-to-end tests for vscode debugger extension?

Question

I've developed a debugger extension for a certain language. Now I want to write some end-to-end tests for the extension. But I've got some troubles on this. I followed the document here: https://code.visualstudio.com/api/working-with-extensions/testing-extension and found out the way to start a debug session by using the startDebugging API. The problem is the API only returns boolean value which indicates whether the debugging starts successfully, but what I need is to get the output in debug console so I can check the final results for different debug configurations. There seems no API like this in the document. So I wonder to know what's the solution for my case here and more generally how to do end-to-end tests for debugger extensions ?