correct...neutral is the best for bearded iris....slightly acidic for most beardless,. ph test kits (usually the "litmus paper strip" kind, are cheap, and fairly accurate...…..the "electronic" ph testers are "fairly" accurate, too. To get an accurate test....the ph of the water used must be factored in. There is a direct link between soil ph, buffer ph, and the soil's ability to "process" nutrients. i'e. your soil could have ample nitrogen, but if the ph is far enough "off", the plants can't USE the nitrogen. Same thing with the ratio of nitrogen to phosphorous....if it's not "within specs", the plant can't use the phosphorous , even though it's in the soil.
There are places that test soil.....you can probably google , and find some locally, or contact your county extension agent, and they can "hook you up" with one. The place I use charges $18 per sample....you get ph, N, P, K, organic content, and a couple trace minerals, and also , it's broken down to tell you, How much lime, (for example) to add per 100 square feet, to arrive at "optimum". Same for the N, K, &P. If you want to spend a bit more, you can get "more trace minerals" tested.
