model.test.js

  'mixed fun': function () {
    var db = start()
      , Post = db.model('BlogPost', collection);

    var post = new Post;
    post.mixed = { x: { one: 1, two: 2 } };
    post.markModified('mixed');
    post.save(function (err) {
      should.strictEqual(err, null);
      Post.findById(post._id, function (err, post) {
        should.strictEqual(err, null);
        post.mixed.should.eql({ x: { one: 1, two: 2 }});
        post.mixed.x.one = "one";
        post.markModified('mixed');
        post.save(function (err, post) {
          db.close();
          should.strictEqual(err, null);
          post.mixed.should.eql({ x: { one: "one", two: 2 }});
        });
      });
    });
  }