message: add nested tape, acc test (fails for now)
diff: @@ -1041,6 +1041,28 @@ class BatchTests(test.TestCase, parameterized.TestCase):
  z = x * y
  self.assertAllClose(acc.jvp(z), constant_op.constant([5.0, 2.0, 7.0]))
  + @parameterized.named_parameters(
  + [("ForwardPropFirst", True),
  + ("TapeFirst", False)])
  + def testBatchBackwardOverForward(self, forward_prop_first):
  + primals = constant_op.constant(1.)
  + tangents = constant_op.constant([.1, .2])
  + expected = constant_op.constant([-.1 * math_ops.cos(1.).numpy(), -.2 * math_ops.cos(1.).numpy()])
  + print(expected)
  + if forward_prop_first:
  + forward_accumulator = forwardprop.ForwardAccumulator._batch_accumulator(primals, tangents)
  + gradient_tape = backprop.GradientTape()
  + else:
  + gradient_tape = backprop.GradientTape()
  + forward_accumulator = forwardprop.ForwardAccumulator._batch_accumulator(primals, tangents)
  + with gradient_tape as tape:
  + with forward_accumulator as acc:
  + tape.watch(primals)
  + d = math_ops.cos(primals)
  + self.assertTrue(tape_lib.should_record_backprop((acc.jvp(d),)))
  + self.assertAllClose(expected,
  + tape.gradient(acc.jvp(d), primals))
  +
  if __name__ == "__main__":
  # TODO(allenl): Also test with 1.x-style graph mode.
  