code: def testMergeCategorical(self):
      actual = mutual_information_util._merge_categorical(
          [
              np.array(["a", "b", "c"]),
              np.array(["1", "2", "3"]),
              np.array(["alpha", "beta", "gamma"]),
          ]
      )
      self.assertTrue(
          np.array_equal(
              np.array([b"a:1:alpha", b"b:2:beta", b"c:3:gamma"]),
              actual,
          )
      )
  
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 15 for calling the RanklabMutualInformationTest obj's underlying member method code with example usage: obj.testMergeCategorical() without return types