code: def test_double(self):
      gv = pyvips.GValue()
      gv.set_type(pyvips.GValue.gdouble_type)
      gv.set(3.1415)
      value = gv.get()
      assert value == 3.1415
  
file_path: pyvips/tests/test_gvalue.py
imports: import pytest
  import pyvips
  from helpers import JPEG_FILE, assert_almost_equal_objects
label_desc: Use image node_id 4 for calling the TestGValue obj's underlying member method code with example usage: obj.test_double() without return types