code: def test_single_step(self):
      with self.strategy.scope():
          optimizer = SGD(
              learning_rate=0.5,
              momentum=0.06,
          )
          grads = tf.constant([1.0, 6.0, 7.0, 2.0])
          vars = backend.Variable([1.0, 2.0, 3.0, 4.0])
  
          self.strategy.run(
              lambda: optimizer.apply_gradients(zip([grads], [vars]))
          )
          self.assertAllClose(
              vars, [0.5, -1.0, -0.5, 3.0], rtol=1e-4, atol=1e-4
          )
  
file_path: keras/keras/backend/tensorflow/optimizer_distribute_test.py
imports: import numpy
  import pytest
  import tensorflow
  from tensorflow.python.eager import context
  from keras import backend
  from keras import testing
  from keras.optimizers.sgd import SGD
label_desc: Use image node_id 3 for calling the OptimizerDistributeTest obj's underlying member method code with example usage: obj.test_single_step() without return types