code: def test_loss(self):
      head = MaskFormerFusionHead(
          num_things_classes=2, num_stuff_classes=2
      )
      result = head.loss()
      self.assertTrue(not head.with_loss)
      self.assertDictEqual(result, dict())
  
file_path: mmdetection/tests/test_models/test_seg_heads/test_maskformer_fusion_head.py
imports: import unittest
  import torch
  from mmengine.config import Config
  from mmdet.models.seg_heads.panoptic_fusion_heads import MaskFormerFusionHead
  from mmdet.structures import DetDataSample
label_desc: Use image node_id 1 for calling the TestMaskFormerFusionHead obj's underlying member method code with example usage: obj.test_loss() without return types