code: def test_construct_vol_no_covar_vol_callable(self):
      vol_fn = tf.sin
      _, total_cov = bm_utils.construct_vol_data(
          vol_fn, None, 1, tf.float32
      )
      self.assertIsNone(total_cov)
  
imports: import numpy
  import tensorflow.compat.v2
  from tensorflow.python.framework import test_util
  from tf_quant_finance.models.legacy import brownian_motion_utils
label_desc: Use image node_id 12 for calling the BrownianMotionUtilsTest obj's underlying member method code with example usage: obj.test_construct_vol_no_covar_vol_callable() without return types