In the present work a modular simulation-based technique for the automatic verification of logic control functions is introduced and exploited to define a structured bottom-up methodology for the testing of the overall control functions of process and power plants. The proposed method has been implemented in a CACSD environment which uses the Matlab toolboxes Simulink and Stateflow for the control functions testing via simulation. The testing of the control logic functions of a portion of a thermal power plant is considered as an application example of the proposed framework.