code: def test_apply_in_pandas_returning_column_names(self):
      self._test_merge(
          fn=lambda lft, rgt: pd.merge(lft, rgt, on=["id", "k"])
      )
  
imports: import unittest
  from typing import cast
  from pyspark.sql.functions import array, explode, col, lit, udf, pandas_udf, sum
  from pyspark.sql.types import ArrayType, DoubleType, LongType, StructType, StructField, YearMonthIntervalType, Row
  from pyspark.sql.window import Window
  from pyspark.errors import IllegalArgumentException, PythonException
  from pyspark.testing.sqlutils import ReusedSQLTestCase, have_pandas, have_pyarrow, pandas_requirement_message, pyarrow_requirement_message
  from pyspark.testing.utils import QuietTest
label_desc: Use image node_id 14 for calling the CogroupedApplyInPandasTestsMixin obj's underlying member method code with example usage: obj.test_apply_in_pandas_returning_column_names() without return types