  We present, for the first time, an observational test of the consistency
relation for the large-scale structure (LSS) of the Universe through a joint
analysis of the anisotropic two- and three-point correlation functions (2PCF
and 3PCF) of galaxies. We parameterise the breakdown of the LSS consistency
relation in the squeezed limit by $E_{\rm s}$, which represents the ratio of
the coefficients of the shift terms in the second-order density and velocity
fluctuations. $E_{\rm s}\neq1$ is a sufficient condition under which the LSS
consistency relation is violated. A novel aspect of this work is that we
constrain $E_{\rm s}$ by obtaining information about the nonlinear velocity
field from the quadrupole component of the 3PCF without taking the squeezed
limit. Using the galaxy catalogues in the Baryon Oscillation Spectroscopic
Survey (BOSS) Data Release 12, we obtain $E_{\rm s} = -0.92_{-3.26}^{+3.13}$,
indicating that there is no violation of the LSS consistency relation in our
analysis within the statistical errors. Our parameterisation is general enough
that our constraint can be applied to a wide range of theories, such as
multicomponent fluids, modified gravity theories, and their associated galaxy
bias effects. Our analysis opens a new observational window to test the
fundamental physics using the anisotropic higher-order correlation functions of
galaxy clustering.
