code: def test_gru_cell(self, backend):
      with fastmath.use_backend(backend):
          layer = tl.GRUCell(9)
          xs = [np.ones((8, 7, 9)), np.ones((8, 7, 9))]
          _, _ = layer.init(shapes.signature(xs))
          ys = layer(xs)
          self.assertEqual(
              [y.shape for y in ys], [(8, 7, 9), (8, 7, 9)]
          )
  
file_path: trax/trax/layers/rnn_test.py
imports: from absl.testing import absltest
  from absl.testing import parameterized
  import numpy
  from trax import fastmath
  from trax import shapes
  import trax.layers
label_desc: Use image node_id 2 for calling the RnnTest obj's underlying member method code with example usage: obj.test_gru_cell(backend) without return types