code: def test_rolling_trend_window_length_less_than_three(
      window_series_pd,
  ):
      primitive_instance = RollingTrend(window_length=2)
  
      vals = primitive_instance(
          window_series_pd.index, window_series_pd.values
      )
  
      for v in vals:
          assert np.isnan(v)
  
file_path: featuretools/featuretools/tests/primitive_tests/aggregation_primitive_tests/test_rolling_primitive.py
imports: import numpy
  import pandas
  import pytest
  from featuretools.primitives import RollingCount, RollingMax, RollingMean, RollingMin, RollingOutlierCount, RollingSTD, RollingTrend
  from featuretools.primitives.standard.transform.time_series.utils import apply_rolling_agg_to_series
  from featuretools.tests.primitive_tests.utils import get_number_from_offset
label_desc: Use image node_id 9 for calling a global function with example usage: test_rolling_trend_window_length_less_than_three(window_series_pd) without return types