Integration testing of programs based on formal specifications can benefit considerably from the comprehensibility of specifications. In this paper, we describe an approach to testing programs based on data-flow-oriented specifications by analyzing data flow paths and discussing criteria for test case generation. This approach suggests a specific way to generate test cases directly from formalized data flow diagrams and the associated textual specifications. We apply the approach in a case study of testing part of an ATM system to evaluate its effectiveness in fault detection and to uncover its weakness for further improvement.