code: def test_sort_values_empty_string(by):
      df = cudf.DataFrame({"a": [3, 2, 1, 4], "b": [""] * 4})
      ddf = dd.from_pandas(df, npartitions=2)
      got = ddf.sort_values(by)
      if "a" in by:
          expect = df.sort_values(by)
          assert dd.assert_eq(got, expect, check_index=False)
  
file_path: cudf/python/dask_cudf/dask_cudf/tests/test_sort.py
imports: import cupy
  import numpy
  import pytest
  import dask
  from dask import dataframe
  import cudf
  import dask_cudf
label_desc: Use image node_id 6 for calling a global function with example usage: test_sort_values_empty_string(by) without return types