jstest is a lightweight unit testing library for javascript. Here's an example:

var task;

jstest("Testing the gearquery module", {
    setup: function(){
        task = gearquery("task", {});
    },

    testExists: function(){
        assert(task, "should not be null");
    },

    testUpdate: function(){
        task.update({name: "Test"}, {where: "id = 2"});
        var name = task.get({id: 2}).name;
        assert(name == "Test");
    }
});

jstest is still currently in alpha mode. I've been using it in Firefox 2.5 and Safari 3 so far, but haven't tested it under IE6 or IE7 yet.

If you run into any bugs or want to give some feedback please email me at hugh (at) hughbien (dot) com.