code: def test_ngpu(self):
      model = neural_gpu.NeuralGPU(d_feature=30, steps=4, vocab_size=22)
      x = np.ones((3, 5, 7)).astype(np.int32)
      _, _ = model.init(shapes.signature(x))
      y = model(x)
      self.assertEqual(y.shape, (3, 5, 7, 22))
  
imports: from absl.testing import absltest
  import numpy
  from trax import shapes
  from trax.models import neural_gpu
label_desc: Use image node_id 1 for calling the NeuralGPUTest obj's underlying member method code with example usage: obj.test_ngpu() without return types