Mocks for light curves and microlensing variations, as well as N-body hydro simulations of lens galaxies are used to test all possible sources of systematic errors. Eventually, a full end-to-end simulation chain will be created to generate a detailed account of all sources of errors.
The results from all the steps are combined together to infer the value of the Hubble parameter within standard or more exotic cosmological models. The analysis steps must be blinded, i.e. carried out without any knowledge of the derived Hubble constant, to avoid the confirmation bias.