If that is all the raised beds have ever had in them, then there isn't any actual "soil" (aka garden dirt) involved. So nothing to test. The MG stuff does have a very low dose fertilizer included but doubt that will be sufficient on its own for a productive season. And especially if you are not adding more MG this year.

I'd add a quantity of compost if I could but also wonder about the lack of minerals in the soil mix. Fertilizing routinely with a full service product (including all trace elements and micronutrients) might solve all the issues you are encountering.

Well, if you're adding an amendment to soil, of course you should get it tested. You don't need to do it every year, but every bed should be tested once just to find out where you stand. You could also just ask neighbors, to see if their original soil had been tested. Your original soil is pretty much the same as theirs. You might consult your local extension service to see if local soils are known to be deficient in something. As noted, the fertilizer content of MG Garden Soil is pretty minimal.

I'm hoping you're not planting exclusively in MG Garden Soil. Might as well just be planting in compost, which is not advisable. The instructions for the stuff say that it should be used in a 50:50 mix with native soil. It is NOT for containers, and is specifically to be added to in-ground garden soil.

I should add that "soil" is stuff you plant in, and you certainly shouldn't be planting anything in pure MG Garden Soil, even according to their own instructions. So the name of the product is a bit confusing.

Bagged "garden soil" is meant to be mixed with other stuff, including your ground dirt or other matter, for use, not meant to be used the way it comes in the bag.

Although you say there is enough and no more is needed, but it's not unheard of to remove some of the soil and mix in other components or thing also, in case that is something you want to do.
I'd also suggest to do some composting , and use those amendments for your garden every year. You can also do trench composting directly into your beds if the local critters are not so bad or you don't have space for larger piles of compost.

To follow up with the other comments - it sounds like you have a soil amendment on top of your actual soil. I would suggest dig down with a spade into the actual soil and turn that over and blend it in to the MG amendment. The combination of the two should be better than leaving them one on top of the other.

Once they are blended, that is the mixture that you want to test.

If you are not going to test, it is a rule of thumb that heavy feeding annuals like vegetables pull nutrients out of the soil that must be replaced in some way every year. If you are doing organic gardening, look for a complete organic fertilzer like Espoma Garden-tone or Dr Earth Tomato Vegetable fertilizer. Apply that in the early spring because the organic ingredients need to be broken down in the soil before the NPK is available to plants in May and June.