Twilio Example

jest.test.ts

namespace Twilio {
    Device = {
        setup: function () { },
        ready: function () { },
        offline: function () { },
        incoming: function () { },
        connect: function (params): Twilio.Connection { return null },
        error: function () { }
    }
}

namespace NodeJS {
    interface Global {
        Twilio : {
            Device : Twilio.IDevice;
        };
    }
}


beforeEach(() => {
    Twilio.Device.setup = () => {return null;};
})

test('adds stuff', () => {
    expect(Twilio.Device).toBeTruthy()
    expect(Twilio.Device.setup(null, null)).toBeNull()
})

twilio.d.ts

declare namespace Twilio {

    class Connection {
        // Constructor does not appear to be available to user.
        private constructor();
        // Add Connection Methods and Properties Here
    }

    type DeviceCallback = (device : IDevice) => void;


    // Not immediately clear if Twilio.Device is a class or not.
    interface IDevice {
        setup(token, options);
        ready(handler: DeviceCallback) : void;
        offline(handler : DeviceCallback) : void;
        error(handler : DeviceCallback) : void;
        incoming(handler);
        connect(params) : Connection;
        // Add Remainder of Twilio.Device properties here.
    }

    /**
     * Twilio.Device appears to be a singleton object that 
     * you don't instantiate yourself. You can use
     * the below to declare its presence.
     */
    let Device : IDevice;
}