message: Explain the comparison used by `assertAllClose`.
diff: @@ -2474,6 +2474,13 @@ class TensorFlowTestCase(googletest.TestCase):
  `a` and `b` can be arbitrarily nested structures. A layer of a nested
  structure can be a `dict`, `namedtuple`, `tuple` or `list`.
  + Note: the implementation follows
  + [`numpy.allclose`](https://docs.scipy.org/doc/numpy/reference/generated/numpy.allclose.html)
  + (and numpy.testing.assert_allclose). It checks whether two arrays are
  + element-wise equal within a tolerance. The relative difference
  + (`rtol * abs(b)`) and the absolute difference `atol` are added together
  + to compare against the absolute difference between `a` and `b`.
  +
  Args:
  a: The expected numpy `ndarray`, or anything that can be converted into a
  numpy `ndarray` (including Tensor), or any arbitrarily nested of
  