The Klyachko inequality is an inequality for the probabiities of the values

of five observables of a spin-1 particle, which is satisfied by any

noncontextual assignment of values to this set of observables, but is violated

by the probabilities defined by a certain quantum state. We describe an

experiment between two entangled spin-1 particles to test contextuality via a

related inequality. We point out that a test of contextuality by measurements

on a single particle to confirm the Klyachko inequality requires an assumption

of non-disturbance by the measuring instrument, which is avoided in the

two-particle experiment.