code: def test_reference_m1(self):
      x = ["A", "A", "B", "B"]
      y = [1, 1, 0, 1]
      x_t = ["A", "B", "C"]
  
      encoder = encoders.MEstimateEncoder(
          m=1, handle_unknown="value", handle_missing="value"
      )
      encoder.fit(x, y)
      scored = encoder.transform(x_t)
  
      expected = [
          [(2 + 3.0 / 4.0) / (2 + 1)],
          [(1 + 3.0 / 4.0) / (2 + 1)],
          [3.0 / 4.0],
      ]  # The prior probability
      self.assertEqual(scored.to_numpy().tolist(), expected)
  
imports: from unittest import TestCase
  import category_encoders
label_desc: Use image node_id 2 for calling the TestMEstimateEncoder obj's underlying member method code with example usage: obj.test_reference_m1() without return types