code: def test_leave_one_out_unique(self):
      X = pd.DataFrame(data=["1", "2", "2", "2", "3"], columns=["col"])
      y = np.array([1, 0, 1, 0, 1])
  
      encoder = encoders.LeaveOneOutEncoder(handle_unknown="value")
      result = encoder.fit(X, y).transform(X, y)
  
      self.assertFalse(
          result.isna().any().any(),
          "There should not be any missing value",
      )
      expected = pd.DataFrame(
          data=[y.mean(), 0.5, 0, 0.5, y.mean()], columns=["col"]
      )
      pd.testing.assert_frame_equal(expected, result)
  
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 4 for calling the TestLeaveOneOutEncoder obj's underlying member method code with example usage: obj.test_leave_one_out_unique() without return types