code: def test_merge_one_chunk():
      df1 = pd.DataFrame(
          {"lkey": ["foo", "bar", "baz", "foo"], "value": [1, 2, 3, 5]}
      )
      df2 = pd.DataFrame(
          {"rkey": ["foo", "bar", "baz", "foo"], "value": [5, 6, 7, 8]}
      )
  
      # all have one chunk
      mdf1 = from_pandas(df1)
      mdf2 = from_pandas(df2)
      df = mdf1.merge(mdf2, left_on="lkey", right_on="rkey")
      tiled, tiled1, tiled2 = tile(df, mdf1, mdf2)
  
      assert tiled.chunk_shape == (1, 1)
      assert tiled.chunks[0].inputs[0].key == tiled1.chunks[0].key
      assert tiled.chunks[0].inputs[1].key == tiled2.chunks[0].key
  
      # left has one chunk
      mdf1 = from_pandas(df1)
      mdf2 = from_pandas(df2, chunk_size=2)
      df = mdf1.merge(mdf2, left_on="lkey", right_on="rkey")
      tiled, tiled1, tiled2 = tile(df, mdf1, mdf2)
  
      assert tiled.chunk_shape == (2, 1)
      assert tiled.chunks[0].inputs[0].key == tiled1.chunks[0].key
      assert tiled.chunks[0].inputs[1].key == tiled2.chunks[0].key
      assert tiled.chunks[1].inputs[0].key == tiled1.chunks[0].key
      assert tiled.chunks[1].inputs[1].key == tiled2.chunks[1].key
  
      # right has one chunk
      mdf1 = from_pandas(df1, chunk_size=2)
      mdf2 = from_pandas(df2)
      df = mdf1.merge(mdf2, left_on="lkey", right_on="rkey")
      tiled, tiled1, tiled2 = tile(df, mdf1, mdf2)
  
      assert tiled.chunk_shape == (2, 1)
      assert tiled.chunks[0].inputs[0].key == tiled1.chunks[0].key
      assert tiled.chunks[0].inputs[1].key == tiled2.chunks[0].key
      assert tiled.chunks[1].inputs[0].key == tiled1.chunks[1].key
      assert tiled.chunks[1].inputs[1].key == tiled2.chunks[0].key
  
file_path: mars/mars/dataframe/merge/tests/test_merge.py
imports: import numpy
  import pandas
  import pytest
  from ....core import tile
  from ....core.operand import OperandStage
  from ...core import IndexValue
  from ...datasource.dataframe import from_pandas
  from ..None import DataFrameMergeAlign, DataFrameMerge, concat
label_desc: Use image node_id 5 for calling a global function with example usage: test_merge_one_chunk() without return types