code: def test_df_stack_mixed_dtypes():
      pdf = pd.DataFrame(
          {
              "A": pd.Series([1, 2, 3], dtype="f4"),
              "B": pd.Series([4, 5, 6], dtype="f8"),
          }
      )
  
      gdf = cudf.from_pandas(pdf)
  
      got = gdf.stack()
      expect = pdf.stack()
  
      assert_eq(expect, got, check_dtype=False)
  
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 6 for calling a global function with example usage: test_df_stack_mixed_dtypes() without return types