How to run a configuration file before executing mocha tests

I have a nodejs function in which I am doing integration tests on visual studio code.

In order for this to work I need a config.js file to run before the test are executed because it initiates the global.gConfig variable ( this is a global variable), which contains all the endpoints the function refers and should connect to either via http or other protocols.

Unfortunately, BeforeEach does not work cause an undefined error is thrown at compilation time. If I initiate the global.gConfig on the file the function runs, it runs ok but I would really want to avoid that.