The main goal of Fiddle, a distributed debugging engine, is to provide a flexible platform for developing debugging tools. Fiddle provides a layered set of interfaces with a minimal set of debugging functionalities, for the inspection and control of distributed and multi-threaded applications. This paper illustrates how Fiddle is used to support integrated testing and debugging. The approach described is based on a tool, called Deipa, that interprets sequences of commands read from an input file, generated by an independent testing tool. Deipa acts as a Fiddle client, in order to enforce specific execution paths in a distributed PVM program. Other Fiddle clients may be used along with Deipa for the fine debugging at process level. Fiddle and Deipa functionalities and architectures are described, and a working example shows a step-by-step application of these tools.