code: def test_load_windpower():
      """Tests load_windpower function."""
      dl = DataLoader()
      df = dl.load_windpower()
      assert list(df.columns) == ["ts", "y"]
      assert df.shape == (8220, 2)
  
      agg_func = {"y": "mean"}
      df = dl.load_windpower(agg_freq="daily", agg_func=agg_func)
      assert TIME_COL in df.columns
      assert df.shape == (343, 2)
      df = dl.load_windpower(agg_freq="weekly", agg_func=agg_func)
      assert TIME_COL in df.columns
      assert df.shape == (50, 2)
      df = dl.load_windpower(agg_freq="monthly", agg_func=agg_func)
      assert TIME_COL in df.columns
      assert df.shape == (12, 2)
  
imports: import os
  import re
  import pandas
  import pytest
  from greykite.common.constants import TIME_COL
  from greykite.common.data_loader import DataLoader
  from greykite.common.testing_utils import assert_equal
label_desc: Use image node_id 12 for calling a global function with example usage: test_load_windpower() without return types