serve as (something)
To act in the capacity of a particular role. I served as a legal secretary for a couple of years while I worked on my law degree. I couldn't even afford furniture, so I just had empty boxes and stacks of books acting as my tables and chairs. We'll have a limited release the product and let this region serve as a guinea pig. If it is received well, we can expand production and distribution to the rest of the county.
serve as someone or something
to act in the capacity of someone or something. I served as the mayor's assistant for a number of years. This brick will not serve as a doorstop.