code: def test_coalesce_without_delete():
      """Test output if nulls remain and `default_value` is provided."""
      df = pd.DataFrame(
          {"s1": [np.nan, np.nan, 6, 9, 9], "s2": [np.nan, 8, 7, 9, 9]}
      )
      expected = df.assign(s3=df.s1.combine_first(df.s2).fillna(0))
      result = df.coalesce(
          "s1", "s2", target_column_name="s3", default_value=0
      )
      assert_frame_equal(result, expected)
  
file_path: pyjanitor/tests/functions/test_coalesce.py
imports: import numpy
  import pandas
  import pytest
  from pandas.testing import assert_frame_equal
label_desc: Use image node_id 8 for calling a global function with example usage: test_coalesce_without_delete() without return types