Last week, we had the author of TDD for a Shopping Website LiveProject. Friday at 11am Ranch time, Steven Solomon will be hosting a live TDD session just for us. See for the agenda and registration link
The only way to get a value from the client to the server is to submit a request, and send that value as a request parameter.
Most often that is done by clicking a link / submitting a form.
With a link, you construct the URL with the parameter dynamically: eg
With submitting a form, you normally put a hidden field onto the page (<input type="hidden") and then submit the form.