code: def test_slots(self):
      weights_shape = (3, 5)
      weight_tree = np.arange(15).reshape(weights_shape)
  
      # SGD - an optimizer that doesn't use slots.
      opt_1 = optimizers.SGD(0.01)
      self.assertIsNone(opt_1.slots)
      opt_1.tree_init(weight_tree)
      self.assertIsInstance(opt_1.slots, tuple)
      self.assertLen(opt_1.slots, 1)
      self.assertIsNone(opt_1.slots[0])
  
      # Momentum - an optimizer with slots
      opt_2 = momentum.Momentum(0.01)
      self.assertIsNone(opt_2.slots)
      opt_2.tree_init(weight_tree)
      self.assertIsInstance(opt_2.slots, tuple)
      self.assertLen(opt_2.slots, 1)
      self.assertEqual(weights_shape, opt_2.slots[0].shape)
  
imports: from absl.testing import absltest
  import numpy
  from trax import optimizers
  from trax.optimizers import momentum
label_desc: Use image node_id 1 for calling the OptimizersTest obj's underlying member method code with example usage: obj.test_slots() without return types