EMC testing of unenclosed PCB assembly
You can make single board products with fast electronics pass CE/FCC in plastic or no housing. 

It is easier if you:


keep all cables attached in one end only
use fewer cables
specify a specific simple application for the FCC/CE test
don't have things that stick off the board (display, large connectors etc.)
make a very low impedance power distribution network (PDN)
have good filtering on the interfaces off the board


It is very difficult if you have multiple boards (plug-in, stacked, cable connected etc.). Actually I would specify a Faraday cage type box if you have multiple boards.

If you absolutely must include a display - try to get one with LVDS interface.

If you have a radio as part of your design, some of this becomes a bit more complex.

I suspect many go fairly light on the CE/FCC thing and self-certify with limited time spent on measurements. It is highly unlikely anyone will ever sue you for an eval board that is out of FCC/CE spec and most of these boards runs in fairly limited volumes. 

Also: I have seen some outfits in China offer to do very cheap CE/FCC marking for you. You get the paperwork - they get some money. Win-win. :-)