Testing is the easy part, but interpreting the results can be confusing.
To help sort out the confusion, this article discusses the reasons for testing, explains the various numbers on the report, considers the advantages and disadvantages of home test kits, and describes a few alternative tests being used by some organic growers. If your garden is growing well, an argument could be made not to bother testing at all. However, if your plants aren't growing as well as you'd like or you're wondering if you're using the right amount of fertilizer, a soil test is the place to start. It will give you a periodic snapshot of your soil's mineral health. This way, you're comparing apples to apples with each set of results.