code: def test_nested_stack(self):
      inp = [
          {"a": ([0, 1], 2), "b": _TestNamedtuple(3)},
          {"a": ([1, 2], 3), "b": _TestNamedtuple(4)},
      ]
      out = {
          "a": ([[0, 1], [1, 2]], [2, 3]),
          "b": _TestNamedtuple([3, 4]),
      }
      onp.testing.assert_equal(fastmath.nested_stack(inp), out)
  
imports: import collections
  from absl.testing import parameterized
  import gin
  import jax.numpy
  import numpy
  from tensorflow import test
  from trax import fastmath
label_desc: Use image node_id 8 for calling the BackendTest obj's underlying member method code with example usage: obj.test_nested_stack() without return types