Unlike traditional way if user design the best way to do is to do paper protyping and then we do development.
User testing is done with end user sometimes and sometimes with client. Another approach followed by team was to give it to other people not part of the project.
Traditionally the focus is to have complete CSS ready.
Ux can be developed in incremental fashion rather than big bang. Some snapshots are below. Similar code cab be reuses. Developers and UI developers can work together.
QA, BAs, Developers and all the related members are updated and mor collaboration is done