code: def test_fillna_nonconsolidated_frame():
      # https://github.com/pandas-dev/pandas/issues/36495
      df = DataFrame(
          [
              [1, 1, 1, 1.0],
              [2, 2, 2, 2.0],
              [3, 3, 3, 3.0],
          ],
          columns=["i1", "i2", "i3", "f1"],
      )
      df_nonconsol = df.pivot(index="i1", columns="i2")
      result = df_nonconsol.fillna(0)
      assert result.isna().sum().sum() == 0
  
imports: import numpy
  import pytest
  from pandas._config import using_pyarrow_string_dtype
  from pandas import Categorical, DataFrame, DatetimeIndex, NaT, PeriodIndex, Series, TimedeltaIndex, Timestamp, date_range, to_datetime
  import pandas._testing
  from pandas.tests.frame.common import _check_mixed_float
label_desc: Use image node_id 1 for calling a global function with example usage: test_fillna_nonconsolidated_frame() without return types