code: def test_TimeSeriesConcatenator():
      """Test the time series concatenator."""
      X, y = load_basic_motions(split="train", return_X_y=True)
  
      # check that loaded dataframe is multivariate
      assert X.shape[1] > 1
  
      trans = ColumnConcatenator()
  
      Xt = trans.fit_transform(X)
  
      # check if transformed dataframe is univariate
      assert Xt.shape[1] == 1
  
      # check if number of time series observations are correct
      n_obs = np.sum([X.loc[0, col].shape[0] for col in X])
      assert Xt.iloc[0, 0].shape[0] == n_obs
  
      # check specific observations
      assert X.iloc[0, -1].iloc[-3] == Xt.iloc[0, 0].iloc[-3]
      assert X.iloc[0, 0].iloc[3] == Xt.iloc[0, 0].iloc[3]
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_TimeSeriesConcatenator() without return types