code: def test_string():
      df = pd.DataFrame(dict(a=[1], b=[2], c=["a"], d=[True]))
      data_id, column_type = "1", "string"
      build_data_inst({data_id: df})
  
      cfg = {"cols": list(df.columns), "joinChar": "-"}
      builder = ColumnBuilder(data_id, column_type, "Col1", cfg)
      verify_builder(
          builder, lambda col: col.values[-1] == "1-2-a-True"
      )
  
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 10 for calling a global function with example usage: test_string() without return types