docstr: MTCNN successfully reports an empty list when no faces are detected.
  :return:
code: def test_detect_no_faces_on_no_faces_content(self):
      """
      MTCNN successfully reports an empty list when no faces are detected.
      :return:
      """
      ivan = cv2.imread("no-faces.jpg")
  
      result = mtcnn.detect_faces(ivan)  # type: list
      self.assertEqual(len(result), 0)
  
file_path: mtcnn/tests/test_mtcnn.py
imports: import unittest
  import cv2
  from mtcnn.exceptions import InvalidImage
  from mtcnn import MTCNN
label_desc: Use image node_id 4 for calling the TestMTCNN obj's underlying member method code with example usage: obj.test_detect_no_faces_on_no_faces_content() without return types