code: def test_mean_prediction_single():
      y_pred = [42]
      y_true = None
  
      result = metrics.mean_prediction(y_true, y_pred)
  
      assert result == 42
  
imports: import fairlearn.metrics
label_desc: Use image node_id 2 for calling a global function with example usage: test_mean_prediction_single() without return types