This paper describes a tool for black-box testing of UDP-based distributed Java programs. UDP provides little guarantee for correct delivery of data, and therefore requires the application to verify the integrity of communication according to its needs. Debugging such application is hard, since it is hard to create at will bad network conditions. The tool describes here creates an intermediary layer above the Java API which simulates network noises. It therefore enables stress-testing the application even on a flawless network environment. We describe a field experience of testing an application, using the tool vs. using specially-written testing code. We show the two approaches to be complementary.