code: def pred(true_r, est, u0=None):
      """Just a small tool to build a prediction with appropriate format."""
      return (u0, None, true_r, est, None)
  
file_path: Surprise/tests/test_accuracy.py
imports: from math import sqrt
  import pytest
  from surprise.accuracy import fcp, mae, mse, rmse
label_desc: Use image node_id 1 for calling a global function with example usage: pred(true_r, est, u0) and returns: u0,  None,  true_r,  est,  None