In the coming months and years mm-VLBI observations of supermassive black holes using the Event Horizon Telescope (EHT), most notably of Saggitarius A* and M87, are expected to verify the existence of astrophysical black holes through detection and measurement of the black hole shadow. Although the mathematical description of a black hole shadow is straightforward, its observational appearance is strongly governed by the (thermo)dynamics and geometrical structure of the surrounding accretion flow. This accretion flow, particularly on event horizon-scales, is turbulent and time variable, and must be modelled using general-relativistic magnetohydrodynamical (GRMHD) simulations. The propagation of radiation and therefore the appearance of shadow images, spectra and lightcurves are calculated using GR radiation transport (GRRT). Here we combine GRMHD and GRRT calculations to derive observational predictions of what upcoming VLBI observations of Sagittarius A* are expected to observe, addressing questions concerning variability therein and also discussing the possibility of testing the Kerr black hole hypothesis and constraining other black hole solutions and theories of gravity.