How to stub function that has Exegesis.CreateController?

Actual function:

export const permanentlyFailed = Exegesis.CreateController(async (context: ExegesisContext) => {}

Stubbing Test:

 const deliveryGetDeliveryRateStub = sandbox.stub(Delivery, "getDeliveryRates").withArgs(sinon.match.any).callsFake(() => {
        return "whatever"
    })

expect(deliveryGetDeliveryRateStub.called).to.be.true