code: def test_names(self, backend):
      with fastmath.use_backend(backend):
          layer = tl.LSTM(3)
          self.assertEqual("LSTM_3", str(layer))
          layer = tl.GRU(5)
          self.assertEqual("GRU_5", str(layer))
          layer = tl.SRU(7)
          self.assertEqual("SRU_7", str(layer))
  
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 5 for calling the RnnTest obj's underlying member method code with example usage: obj.test_names(backend) without return types