To cope with the need for flexibility of industrial applications, and other customer related requirements, functional control behavior is shifted from hardware to software. This leads to higher software complexity. Therefore, testing of industrial software is a key technique to ensure overall system quality. Based on an analysis of testing approaches in software engineering and requirements in industrial automation system design with IEC 61499 function blocks a new unit testing process is proposed. The implementation of a platform independent test framework for IEC 61499 function blocks shows the applicability of the proposed testing process with representative examples. The presented solution is the first test framework based on the test first development approach to increase the software quality for industrial automation systems.