In this paper we describe our experience from developing and testing a visual Graphical User Interface (GUI) editor for mobile and multimedia devices. Testing of the editor’s highly interactive user interface is critical for its success, yet remains a challenge due to the specification of often intangible quality characteristics of the GUI and its proneness to change. The approach we provide is supporting exploratory testing of the GUI with tools integrated with the tested object. Thus a step-by-step guide for manual exploratory testing can be enhanced with automated elements that directly manipulate the status of the editor, access in-ternal properties of the GUI, and record interactions for bug reporting.