  We study discrimination of m quantum measurements in the scenario when the
unknown measurement with n outcomes can be used only once. We show that
ancilla-assisted discrimination procedures provide a nontrivial advantage over
simple (ancilla-free) schemes for perfect distinguishability and we prove that
inevitably m <= n. We derive necessary and sufficient conditions of perfect
distinguishability of general binary measurements. We show that the
optimization of the discrimination of projective qubit measurements and their
mixtures with white noise is equivalent to the discrimination of specific
quantum states. In particular, the optimal protocol for discrimination of
projective qubit measurements with fixed failure rate (exploiting maximally
entangled test state) is described. While minimum error discrimination of two
projective qubit measurements can be realized without any need of entanglement,
we show that discrimination of three projective qubit measurements requires a
bipartite probe state. Moreover, when the measurements are not projective, the
non-maximally entangled test states can outperform the maximally entangled
ones.
