code: def test_concatenate():
      df = pd.DataFrame(dict(a=["a"], b=["b"]))
  
      data_id, column_type = "1", "concatenate"
      build_data_inst({data_id: df})
  
      cfg = dict(left=dict(col="a"), right=dict(col="b"))
      builder = ColumnBuilder(data_id, column_type, "a_b", cfg)
      verify_builder(builder, lambda col: col.values[0] == "ab")
  
      cfg = dict(left=dict(col="a"), right=dict(val="b"))
      builder = ColumnBuilder(data_id, column_type, "a_b2", cfg)
      verify_builder(builder, lambda col: col.values[0] == "ab")
  
imports: import numpy
  import pandas
  import pytest
  import sklearn
  from numpy.random import randn
  from pkg_resources import parse_version
  from six import PY3
  import dtale.pandas_util
  from dtale.column_builders import ColumnBuilder, ZERO_STD_ERROR
  from tests.dtale import build_data_inst
label_desc: Use image node_id 20 for calling a global function with example usage: test_concatenate() without return types