code: def test_generate_test_changepoint_df():
      df = generate_test_changepoint_df(
          freq="D",
          periods=200,
          n_changepoints=3,
          signal_strength=1 / 5,
          err_std=1,
      )
      assert df.shape == (200, 2)
      assert not df.isna().any().any()
      assert not df["ts"].isna().any().any()
  
file_path: greykite/greykite/tests/common/test_testing_utils.py
imports: import datetime
  from greykite.common.constants import TIME_COL
  from greykite.common.constants import VALUE_COL
  from greykite.common.testing_utils import generate_df_for_tests
  from greykite.common.testing_utils import generate_df_with_reg_for_tests
  from greykite.common.testing_utils import generate_test_changepoint_df
label_desc: Use image node_id 3 for calling a global function with example usage: test_generate_test_changepoint_df() without return types