code: def test_min_obs_error():
      params = dict(prediction_length=10, prophet_params={})
  
      dataset = ListDataset(
          data_iter=[
              {"start": "2017-01-01", "target": np.array([1.0])}
          ],
          freq="1D",
      )
  
      with pytest.raises(ValueError) as excinfo:
          predictor = ProphetPredictor(**params)
          list(predictor.predict(dataset))
  
      act_error_msg = str(excinfo.value)
      exp_error_msg = "Dataframe has less than 2 non-NaN rows."
  
      assert act_error_msg == exp_error_msg
  
file_path: gluonts/test/ext/prophet/test_prophet.py
imports: import numpy
  import pytest
  from gluonts.core import serde
  from gluonts.dataset.common import ListDataset
  from gluonts.ext.prophet import ProphetPredictor
label_desc: Use image node_id 3 for calling a global function with example usage: test_min_obs_error() without return types