code: def gray2bgr(tens: Tensor) -> Tensor:
      r"""
          Converts a Grayscale Tensor to its BGR version.
  
      Args:
          tens (Tensor): Valid Grayscale Tensor
  
      Returns:
          BGR Tensor of shape ``(height, width, channels)``
  
      Raises:
          ValueError: If `tens` is not of shape 2
  
      """
      if not _is_gray_image(tens):
          raise ValueError(
              f"Tensor of shape 2 expected. Found shape {len(tens.shape)}. "
              "This function converts a Grayscale Tensor to its BGR counterpart"
          )
  
      img = cv.cvtColor(tens, GRAY2BGR)
      return to_tensor(img, cspace="bgr")
  
file_path: caer/caer/color/_gray.py
imports: import cv2
  from ..coreten import Tensor, to_tensor
  from ._constants import GRAY2BGR, GRAY2RGB
  from ._bgr import bgr2lab, bgr2hsv, bgr2hls, bgr2yuv, bgr2luv
label_desc: Use image node_id 3 for calling a global function with example usage: gray2bgr(tens) and returns: to_tensor