code: def test_luv2gray():
      cv_luv = cv.cvtColor(cv_bgr, cv.COLOR_BGR2LUV)
      cv_luv = caer.to_tensor(cv_luv, cspace="luv")
  
      gray = caer.luv2gray(cv_luv)
  
      assert len(gray.shape) == 2 or (
          len(gray.shape) == 3 and gray.shape[-1] == 1
      )
      assert isinstance(gray, caer.Tensor)
      assert gray.is_gray()
  
file_path: caer/tests/color/test_luv.py
imports: import caer
  import cv2
  import os
label_desc: Use image node_id 3 for calling a global function with example usage: test_luv2gray() without return types