code: def test_combines_empty_non_empty(self):
      accumulator1 = variance_util.MeanVarAccumulator()
      accumulator2 = variance_util.MeanVarAccumulator()
      accumulator2.update(np.array([1, 1, 1]))
      accumulator1.merge(accumulator2)
      self.assertEqual(accumulator1.mean, 1)
      self.assertEqual(accumulator1.variance, 0)
  
imports: from absl.testing import absltest
  from absl.testing import parameterized
  import numpy
  from tensorflow_data_validation.utils import variance_util
label_desc: Use image node_id 4 for calling the MeanVarAccumulatorTest obj's underlying member method code with example usage: obj.test_combines_empty_non_empty() without return types