Property testing algorithms exhibit a fascinating connection between global properties of objects and small, local views. Such algorithms are "ultra"-efficient to the extent that they only read a tiny portion of their input, and yet they decide whether a given object has a certain property or is significantly different from any object that has the property. To this end, property testing algorithms are given the ability to perform (local) queries to the input, though the decisions they need to make usually concern properties of a global nature. In the last two decades, property testing...