code: def test_df_where_change_dtype(self):
      # GH#16979
      df = DataFrame(
          np.arange(2 * 3).reshape(2, 3), columns=list("ABC")
      )
      mask = np.array([[True, False, False], [False, False, True]])
  
      result = df.where(mask)
      expected = DataFrame(
          [[0, np.nan, np.nan], [np.nan, np.nan, 5]],
          columns=list("ABC"),
      )
  
      tm.assert_frame_equal(result, expected)
  
imports: from datetime import datetime
  from hypothesis import given
  import numpy
  import pytest
  from pandas.core.dtypes.common import is_scalar
  import pandas
  from pandas import DataFrame, DatetimeIndex, Index, Series, StringDtype, Timestamp, date_range, isna
  import pandas._testing
  from pandas._testing._hypothesis import OPTIONAL_ONE_OF_ALL
label_desc: Use image node_id 25 for calling the TestDataFrameIndexingWhere obj's underlying member method code with example usage: obj.test_df_where_change_dtype() without return types