  One of the most pressing issues in cosmology is whether general relativity
(GR) plus a dark sector is the underlying physical theory or whether a modified
gravity model is needed. Upcoming dark energy experiments designed to probe
dark energy with multiple methods can address this question by comparing the
results of the different methods in constraining dark energy parameters.
Disagreement would signal the breakdown of the assumed model (GR plus dark
energy). We study the power of this consistency test by projecting constraints
in the $w_0-w_a$ plane from the four different techniques of the Dark Energy
Survey in the event that the underlying true model is modified gravity. We find
that the standard technique of looking for overlap has some shortcomings, and
we propose an alternative, more powerful Multi-dimensional Consistency Test. We
introduce the methodology for projecting whether a given experiment will be
able to use this test to distinguish a modified gravity model from GR.
