var someUtilityFunction = () {
    return window.location.search.substring(1);
};

test('#1 someUtilityFunction works', function () {
    // setup
    var oldQS = window.location.search;
    window.location.search = '?key1=value1&key2=value2&key3=value3';

    var expectedOutput = 'key1=value1&key2=value2&key3=value3';

    // test
    equals(someUtilityFunction(),
        expectedOutput,
        'someUtilityFunction works as expected.');

    // teardown
    window.location.search = oldQS;
});

var customWindow = {
    location: {
        search: "",
        hash: ""
    }
};

var someUtilityFunction;

(function(window) {
    // window is now shadowed by your local variable
    someUtilityFunction = () {
        return window.location.search.substring(1);
    };
})(customWindow);

// first some more preparation for our mock
customWindow.window = customWindow;

with(customWindow) {

    // this still creates the var in the global scope
    var someUtilityFunction = () {
        // window is a property of customWindow
        return window.location.search.substring(1);
    };

    // since customWindow is our scope now
    // this will work also
    someUtilityFunction = () {
        // location is a property of customWindow too
        return location.search.substring(1);
    };

}

window.location.search.replace(/^?/, "");

window.location.substr(1);