1. A user-interface testing process comprising: computer-implemented generating of plural display-data representations of a common subject for plural respective user-interface instances executing on plural respective computers; computer-implemented tracking of said display-data representations for each of said user-interface instances so as to generate respective object-level descriptions of said display-data representations; and computer-implemented comparing of said object-level descriptions to detect differences between said user-interface instances in their respective display-data representations of said common subject on different ones of said computers.