Mock a static method from a mongoose model

I made a static method for one a my models and I woudlike to mock it with sinon.

var mongoose = require('mongoose');
var Schema   = mongoose.Schema;

var schema = new Schema({
    name: String
});

schema.static('addName', function (name_id, name) {
    ...
});

module.exports = mongoose.model('Name', schema);

and

addNameSpy = sinon.spy(Name, "addName");

But it doesn't seem to work: the method is called, but addNameSpy.called is still false. Any idea to mock a mongoose static method ?

Thanks.