code: def test_single_step_2d(self):
      optimizer = Adafactor(learning_rate=0.5)
      grads = np.array([[1.0, 6.0], [7.0, 2.0]])
      vars = backend.Variable([[1.0, 2.0], [3.0, 4.0]])
      optimizer.apply_gradients(zip([grads], [vars]))
      self.assertAllClose(
          vars,
          [[0.7007, -0.0081], [1.2492, 3.4407]],
          rtol=1e-4,
          atol=1e-4,
      )
  
file_path: keras/keras/optimizers/adafactor_test.py
imports: import numpy
  from keras import backend
  from keras import testing
  from keras.optimizers.adafactor import Adafactor
label_desc: Use image node_id 3 for calling the AdafactorTest obj's underlying member method code with example usage: obj.test_single_step_2d() without return types