another way

gistfile1.txt

    $(document).ready(function(){
        $('button').click(function() {
            var $button = $(this),
                    test = $button.text() === 'Expand',
                    test2 = $button.text() === 'Collapse';

            if(test)
            {
                $button.text('Collapse');
            }
            else if(test2)
            {
                $button.text('Expand');
            }
        });
    });