  Inspired by a recent classical distribution-free junta tester by Chen, Liu,
Serverdio, Sheng, and Xie (STOC'18), we construct a quantum tester for the same
problem with complexity $O(k/\varepsilon)$, which constitutes a quadratic
improvement.
  We also prove that there is no efficient quantum algorithm for this problem
using quantum examples as opposed to quantum membership queries.
  This result was obtained independently from the $\tilde O(k/\varepsilon)$
algorithm for this problem by Bshouty.
