Change dynamic value demand on checkbox with knockout

I've three elements: selectbox, checkbox, input.

viewModel.listTest= [{ value: '1', name: '10' }, { value: '2', name: '20' }];
<select class="form-control" data-bind="options: listTest, value: TestSelectBox, optionsText: 'name', optionsValue: 'value', disable: TestTrigger()"></select>

viewModel.TestTrigger= ko.observable(false);
<input id="TestTrigger" type="checkbox" name="TestTrigger" data-bind="checked: TestTrigger" /> 

viewModel.inputTest = ko.observable('1');
<input name="inputTest " data-bind="value: inputTest , enable: TestTrigger(), valueUpdate: 'afterkeydown'" />

and I want to make: if checkbox is checked the value from input should pass to

viewModel.testValue 

otherwise the value from select box should be pass to

viewModel.testValue 

How can I do this ? I think I can use knockout method subscribe on checkbox