knockout.js calling custom binding function

I've found an unusual code, but I don't understand how to call this custom binding function and how is that supposed to work. So here is my code:

ViewModel:

ko.bindingHandlers.test = function ($) {
    return {
        init: function (el, valueAccessor, bindingsAccessor, viewModel) {
        },
        update: function (el, valueAccessor, bindingsAccessor, viewModel) {
        }
    }
}

View:

<input type="text" data-bind="test: ???, value: 0, settings: { test: 'test-value' }">

your code is wrong since you have have a closure scope you need todo

ko.bindingHandlers.test = (function ($) {
    return {
        init: function (el, valueAccessor, bindingsAccessor, viewModel) {
        },
        update: function (el, valueAccessor, bindingsAccessor, viewModel) {
        }
    }
})(jQuery);

edit: In your markup bind test to a member on your viewModel like

<input type="text" data-bind="test: myMember />

To access the binding from your custom binding

init: function (el, valueAccessor, bindingsAccessor, viewModel) {
   var value = ko.utils.unwrapObservable(valueAccessor());
}