You can buy a ph soil testing kit - Rapitest make one, but there are others. Otherwise, just have a look around your area to see what's growing well - rhododendrons and azaleas present round and about indicate neutral to acidic, Pieris and Skimmia with healthy green leaves also, as do blue hydrangeas.

Someone recently - I think it was Tugbrethil - gave a very full answer to this to supplement your soil testing kit as it also told you how to find out about clay humus and loam contenet etc. I nominated it for Goypedia but I looked under Soil and it wasn't there.