code: def test_join_on_series(self, target_source):
      target, source = target_source
      result = target.join(source["MergedA"], on="C")
      expected = target.join(source[["MergedA"]], on="C")
      tm.assert_frame_equal(result, expected)
  
imports: import re
  import numpy
  import pytest
  import pandas.util._test_decorators
  import pandas
  from pandas import Categorical, DataFrame, Index, MultiIndex, Series, Timestamp, bdate_range, concat, merge, option_context
  import pandas._testing
label_desc: Use image node_id 19 for calling the TestJoin obj's underlying member method code with example usage: obj.test_join_on_series(target_source) without return types