Testing a first graphical program intended for implementation on a programmable hardware element. The first graphical program may be stored. The first graphical program may include a first plurality of nodes connected by lines which visually specify first functionality. The first graphical program may be intended for implementation by the programmable hardware element. A second graphical program may be stored which visually specifies testing functionality for the first graphical program. The second graphical program may be executable by a host computer to simulate input to the programmable hardware element when configured by the first graphical program. The first graphical program and the second graphical program may be executed (e.g., by a host computer) to test the first functionality when implemented by the programmable hardware element. During execution, simulated outputs may be monitored.