docstr: Tests using preprocessing_layers without preprocessing_combiner.
docstr_tok: ["Tests","using","preprocessing_layers","without","preprocessing_combiner","."]
code: def testPreprocessingLayersSingleObservations(self):
      """Tests using preprocessing_layers without preprocessing_combiner."""
      num_state_dims = 5
      network = q_network.QNetwork(
          input_tensor_spec=tensor_spec.TensorSpec(
              [num_state_dims], tf.float32
          ),
          action_spec=tensor_spec.BoundedTensorSpec(
              [1], tf.int32, 0, 1
          ),
          preprocessing_layers=tf.keras.layers.Lambda(lambda x: x),
          preprocessing_combiner=None,
      )
      q_logits, _ = network(tf.ones((3, num_state_dims)))
      self.assertAllEqual(q_logits.shape.as_list(), [3, 2])
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import gin
  import tensorflow
  from tf_agents.networks import q_network
  from tf_agents.specs import tensor_spec
label_desc: Use image node_id 12 for calling the SingleObservationSingleActionTest obj's underlying member method code with example usage: obj.testPreprocessingLayersSingleObservations() without return types