code: def test_assign_sub(self):
      with hk.variables():
          v = tf.Variable(tf.ones([]))
      v.assign_sub(1.0)
      self.assertAllEqual(v.numpy(), 0)
      self.assertAllEqual(v.read_value().numpy(), 0)
      self.assertAllEqual(v.tensor_value.numpy(), 0)
  
imports: from absl.testing import parameterized
  import sonnet
  from sonnet.src import test_utils
  from sonnet.src.functional import haiku
  import tensorflow
  import tree
label_desc: Use image node_id 12 for calling the TensorVariableTest obj's underlying member method code with example usage: obj.test_assign_sub() without return types