def METHOD_NAME(self):
    """Test the length of detection instance results is 0."""
    from mmengine.config import ConfigDict
    cfg = ConfigDict(
        nms_pre=1000,
        max_per_img=1000,
        nms=dict(type='nms', iou_threshold=0.7),
        min_bbox_size=0)
    rpn_head = RPNHead(num_classes=1, in_channels=1)
    results = InstanceData(metainfo=dict())
    results.bboxes = torch.zeros((0, 4))
    results.scores = torch.zeros(0)
    results = rpn_head._bbox_post_process(results, cfg, img_meta=dict())
    self.assertEqual(len(results), 0)
    self.assertEqual(results.bboxes.size(), (0, 4))
    self.assertEqual(results.scores.size(), (0, ))
    self.assertEqual(results.labels.size(), (0, ))