code: def testUnitVarianceScale(self):
      arr = np.array([1.0, 2.0, np.nan])
      actual = mutual_information_util._unit_variance_scale(arr)
      stdev = np.std([1.0, 2.0], ddof=1)
      self.assertTrue(
          np.allclose(
              np.array([(1.0 - 1.5) / stdev, (2 - 1.5) / stdev]),
              actual[~np.isnan(actual)],
              atol=1e-5,
          )
      )
  
imports: from absl.testing import absltest
  from absl.testing import parameterized
  import numpy
  from tensorflow_data_validation.utils import mutual_information_util
label_desc: Use image node_id 18 for calling the RanklabMutualInformationTest obj's underlying member method code with example usage: obj.testUnitVarianceScale() without return types