jquery.test.html

            <!-- TESTING DEV_CHECKLIST-->
            <script>
                //Will jQuery Be Found?
                if (window.jQuery) {
                    // jQuery is loaded
                    document.write('jQuery is loaded');
                } else {
                    // jQuery is not loaded

                    document.write('jQuery is not loaded');
                }
                if (window.$j) {
                    // jQuery is loaded
                    document.write('$j is loaded');
                } else {
                    // jQuery is not loaded

                    document.write('$J is not loaded');
                }

                $j(document).ready(function(){
                    $j("button.test").click(function(){
                        $j("p.test").text("jQuery works!");
                    });
                });
            </script>


            <div style="border: 1px solid #999; border-radius: 5px; text-align: center; background:#efefef;">
                <p class="test">Check if jQuery is Working.</p>
                <button class="test">Test jQuery</button>
            </div>
            <!-- TESTING -->

Good to check when using multiple libraries, ie. Prototype + jQuery