code: def test_bandjoin(self):
      black = pyvips.Image.black(16, 16)
      a = black.draw_rect(1, 0, 0, 1, 1)
      b = black.draw_rect(2, 0, 0, 1, 1)
      c = black.draw_rect(3, 0, 0, 1, 1)
      im = a.bandjoin([b, c, a, b, c, a, b, c])
  
      assert im.width == 16
      assert im.height == 16
      assert im.bands == 9
  
      x = im.bandjoin([])
      assert x.bands == 9
  
file_path: pyvips/tests/test_image.py
imports: import pyvips
  import pytest
  from helpers import JPEG_FILE
label_desc: Use image node_id 3 for calling the TestImage obj's underlying member method code with example usage: obj.test_bandjoin() without return types