I have 5 raised beds, the soil in which is a combination of equal parts compost, vermiculite and peat moss in which I grow a variety of vegetables. This mixture was suggested by the book "Square Foot Gardening". Is there any reason to have the soil tested and can a lab adequately test this soil mixture?
Yes, you still need to have soil tested every 3-4 years at least, because the pH will change (making nutrients more or less available to the plants) and the quantities of nutrients themselves will change. This will be no problem for a soil testing lab.
Here is our webpage on raised beds (you can click on the red links to soil testing which explains how to do it and gives regional labs to use): https://extension.umd.edu/hgic/topics/raised-beds
Please read through this entire page.