The Deal with Agencies & Test Shoots for Portfolio Building

When you sign with an agency you're well on your way towards a bright and promising modeling career. The first step is to do your first photo shoot for the purpose of building not only your portfolio but your comp card as well. In this day and age of the Internet, many modeling agencies post their models' portfolios online as well the print version of the portfolio, which is commonly referred to as a model's "book." Of course all this costs money but whose supposed to cover those costs? Should anyone have to pay at all? What about test shoots?