Testing Auth.SessionManagement.getCurrentSession() fails

Hello

A newbie trying to test an apex which is using the Auth.SessionManagement.getCurrentSession().
When I invoke the method global Process.PluginResult invoke(Process.PluginRequest request)
from my test class using plugin.invoke(request), the test fails with "System.UnexpectedException: Current session unavailable"

Question is: How to test a method which has an internal call to Auth.SessionManagement.getCurrentSession()

I do not find a way to set the session using the API. Any help is appreciated!