code: def test_check_extra_output_columns_cross_validation(
      self, ts_short, backend, extra_output_columns
  ):
      m = Prophet(stan_backend=backend)
      m.fit(ts_short)
      df_cv = diagnostics.cross_validation(
          m,
          horizon="1 days",
          period="1 days",
          initial="140 days",
          extra_output_columns=extra_output_columns,
      )
      assert "trend" in df_cv.columns
  
imports: import datetime
  import itertools
  import numpy
  import pandas
  import pytest
  from prophet import Prophet, diagnostics
label_desc: Use image node_id 4 for calling the TestCrossValidation obj's underlying member method code with example usage: obj.test_check_extra_output_columns_cross_validation(ts_short, backend, extra_output_columns) without return types