code: def test_HandleMissingIsValueAndNanInTestAndNoTestTarget_ExpectMean(
      self,
  ):
      df = pd.DataFrame(
          {
              "color": ["a", "a", "a", "b", "b", "b"],
              "outcome": [1, 0, 0, 1, 0, 1],
          }
      )
  
      train = df.drop("outcome", axis=1)
      target = df.drop("color", axis=1)
      test = pd.Series([np.nan, "b"], name="color")
  
      ce_leave = encoders.LeaveOneOutEncoder(
          cols=["color"], handle_missing="value"
      )
      ce_leave.fit(train, target["outcome"])
      obtained = ce_leave.transform(test)
  
      self.assertEqual([0.5, 2 / 3.0], list(obtained["color"]))
  
file_path: category_encoders/tests/test_leave_one_out.py
imports: import pandas
  from unittest import TestCase
  import tests.helpers
  import numpy
  import category_encoders
label_desc: Use image node_id 7 for calling the TestLeaveOneOutEncoder obj's underlying member method code with example usage: obj.test_HandleMissingIsValueAndNanInTestAndNoTestTarget_ExpectMean() without return types