Where I work, we made the decision to make all instrument references into LVOOP classes, all of which have a common ancestor with a limited set of required functions (Initialize, Stop, etc.). Our own custom HAL (hardware abstraction layer) implementation. You can find other posts and probably some white papers about other people's implementations.
The part that's relevant to what you're looking for is that once you've created a LVOOP class for your scanner, and made all the VIs in it that communicate with hardware into Dynamic Dispatch, it becomes super simple to create a descendant class that overrides all of the VIs that do hardware communication and replace them with VIs that don't communicate. You can have these descendant classes return hard-coded values, read values from a file to return, or have them interact with other simulated instruments in the background to produce reasonable test values (for example, if you simulate a power supply and a multimeter, you can make it so the value your multimeter reads is dependent on the set point of your power supply, even though neither of them really exist.
Once you've done all that, all you have to do is load in an instance of the simulated LVOOP class instead of the standard one, and then as long as you're passing your references around properly your entire codebase can be tested with simulated instruments with one toggle.
