  Tests of gravity on large-scales in the universe can be made using both
imaging and spectroscopic surveys. The former allow for measurements of weak
lensing, galaxy clustering and cross-correlations such as the ISW effect. The
latter probe galaxy dynamics through redshift space distortions. We use a set
of basic observables, namely lensing power spectra, galaxy-lensing and
galaxy-velocity cross-spectra in multiple redshift bins (including their
covariances), to estimate the ability of upcoming surveys to test gravity
theories. We use a two-parameter description of gravity that allows for the
Poisson equation and the ratio of metric potentials to depart from general
relativity. We find that the combination of imaging and spectroscopic
observables is essential in making robust tests of gravity theories. The range
of scales and redshifts best probed by upcoming surveys is discussed. We also
compare our parametrization to others used in the literature, in particular the
gamma parameter modification of the growth factor.
