code: def test_join_apply():
      df = pd.DataFrame({"a": [1, 2, 3], "b": [2, 3, 4]}).join_apply(
          lambda x: 2 * x["a"] + x["b"], new_column_name="2a+b"
      )
  
      expected = df.copy()
      expected["2a+b"] = [4, 7, 10]
  
      assert_frame_equal(df, expected)
  
imports: import pandas
  import pytest
  from pandas.testing import assert_frame_equal
  import janitor
label_desc: Use image node_id 1 for calling a global function with example usage: test_join_apply() without return types