code: def testMergeEstimators(self):
      estimator1 = size_estimator.SizeEstimator(
          size_threshold=10, size_fn=len
      )
      self.assertEqual(estimator1.get_estimate(), 0)
      estimator2 = size_estimator.SizeEstimator(
          size_threshold=10, size_fn=len
      )
      self.assertEqual(estimator2.get_estimate(), 0)
      a = b"plmjh"
      b, c = a, a
      expected_size_estimate = (
          int(len(a) / (sys.getrefcount(a) - 1)) * 4
      )
      estimator1.update(a)
      estimator1.update(b)
      estimator2.update(c)
      estimator2.update(a)
      estimator1 += estimator2
      self.assertEqual(
          estimator1.get_estimate(), expected_size_estimate
      )
  
imports: import sys
  import tensorflow
  from tensorflow_model_analysis.utils import size_estimator
label_desc: Use image node_id 3 for calling the SizeEstimatorTest obj's underlying member method code with example usage: obj.testMergeEstimators() without return types