Eugenie Reich has an article in Nature News about the use of mock, simulated or fake data in astronomy research on dark matter. The terms are used interchangeably in the piece, but I would choose simulated over the other two. It simply minimizes the chances of misinterpretation by the public. I’m reminded of the mini-firestorm initiated by opponents of climate change policy to references in scientific discussions about using ‘tricks’ to present climate data.
I’m not sure of any opposition (organized or otherwise) to research involving dark matter or dark energy. But I think it could well strike the public as odd, or perhaps counterintuitive, to hear references to fake data in scientific research without reference to fraud or other bad activities. In the instances cited by Reich, the simulated data are used to test algorithms and related methods for identifying galaxies from large data sets gathered by scientific instruments. It would be comparable to using a test weight or other object to calibrate an instrument. I don’t think such calibration or refinement tests are well served by referring to fake or mock data. But I may be overthinking this.