  A locally testable code is an error-correcting code that admits very
efficient probabilistic tests of membership. Tensor codes provide a simple
family of combinatorial constructions of locally testable codes that generalize
the family of Reed-Muller codes. The natural test for tensor codes, the
axis-parallel line vs. point test, plays an essential role in constructions of
probabilistically checkable proofs.
  We analyze the axis-parallel line vs. point test as a two-prover game and
show that the test is sound against quantum provers sharing entanglement. Our
result implies the quantum-soundness of the low individual degree test, which
is an essential component of the MIP* = RE theorem. Our proof also generalizes
to the infinite-dimensional commuting-operator model of quantum provers.
