code: def test_column_selector_empty(data):
      """
      Checks if column selector works
      :param data: iris dataset from pytest.fixture
      """
      df = pd.DataFrame(data, columns=list("abcd"))
      columns = []
      selector = ColumnSelector(columns)
  
      result = selector.fit_transform(df)
      assert result.shape == (df.shape[0], 0)
      assert selector.column_names == columns
  
imports: import pandas
  import pytest
  from sklearn.datasets import load_iris
  from greykite.sklearn.transform.column_selector import ColumnSelector
label_desc: Use image node_id 3 for calling a global function with example usage: test_column_selector_empty(data) without return types