Cypress stub Omniture page tracking function

I'm trying to stub the Omniture page tracking function s.t(). It is called on every page load after some processing is done to set appropriate variables that should be sent with the request. I'm trying to test that the correct variables/tracking parameters are being set on a given page.

Here is what I have tried:

cy.visit();
cy.stub(s, "t");

This just generates an error saying s is not defined. (s is the global object that the Omniture s_code creates).

So after some google searching I found that you have to initialize the object first, so my code turned into this:

var s = {
    t: cy.stub()
};
cy.visit();

That doesn't generate any errors, and shows the stub in the command log but it says the function was never called. I know it was called, because I see the Omniture request in the network tab of the developer console.

Can anyone tell me what I'm doing wrong? It would be much appreciated.