code: def test_unstack_index_invalid():
      gdf = cudf.DataFrame({"a": [1, 2, 3], "b": ["a", "b", "c"]})
      with pytest.raises(
          ValueError,
          match=re.escape(
              "Calling unstack() on single index dataframe with "
              "different column datatype is not supported."
          ),
      ):
          gdf.unstack()
  
imports: import re
  from itertools import chain
  import numpy
  import pandas
  import pytest
  import cudf
  from cudf import melt
  from cudf.core.buffer.spill_manager import get_global_manager
  from cudf.testing._utils import ALL_TYPES, DATETIME_TYPES, NUMERIC_TYPES, assert_eq
label_desc: Use image node_id 20 for calling a global function with example usage: test_unstack_index_invalid() without return types