sapui5 QUnit testing - how to use controller functions in my testcontroller

I am really new to the sapui5 language. And currently I'm starting with Qunit testing. My question is, how can I Import functions from other controlls to my test- controlls? e.g. in python there is an "Import function from module".

this is my test for my configuration.controller

this is my _getParentPath function in my configuration.controller

the thing which isnt working is :

var sState = ConfigurationController._getParentPath(oObj.path);

the test is working I just struggle with that line, because I don't understand how to call my own functions from other controlls.