The ultimate soil test is how well your plants are doing. If your plants are healthy, have plenty of blooms and are producing nice fruits and vegetables, then you probably don't need a soil test. Plants do well in healthy soil. As a general rule, one inch of good compost a year should be enough to grow most annual fruits and vegetables. To help your plants even further, you can spray a kelp formula every other week.
Kelp contains lots of micronutrients and hormones that help plants prosper.
However, if your plants aren't doing well and compost doesn't help, a soil test can help you decide how to improve your soil. To my way of thinking, soil testing of nutrients is good for telling you generalities, but not specifics. Originally nutrient testing was an aid for synthetic chemical farming. With this type of soil, there was not a lot of biological activity to help store nutrients or make them more readily available to plants. Therefore, the determination of nutrient amounts needed to grow a given crop was pretty straight forward.