.... the best thing i've found so far for such test is - toy!
most children toys are very colourful and you can get different sizes - depending on how far you want them to be placed.....
arrange the toys so that you have some of them in your intended sharp focus and some in the background to see how the background blur (aka bokeh) will be like.
set your tripod, focus and shoot away! you may want to try auto-WB and manual-WB to see the different colour response (some lens tends to be stronger/emphasise certain colours!)