docstr: Test corner case where a network might predict no boxes and
  ignore_iof_thr is on.
code: def test_center_region_assigner_with_empty_boxes_and_ignore(self):
      """Test corner case where a network might predict no boxes and
      ignore_iof_thr is on."""
      center_region_assigner = CenterRegionAssigner(
          pos_scale=0.2, neg_scale=0.2, min_pos_iof=0.01
      )
      priors = torch.empty((0, 4))
      gt_bboxes = torch.FloatTensor(
          [
              [0, 0, 10, 9],
              [0, 10, 10, 19],
          ]
      )
      gt_bboxes_ignore = torch.Tensor(
          [
              [30, 30, 40, 40],
          ]
      )
      gt_labels = torch.LongTensor([2, 3])
  
      pred_instances = InstanceData(priors=priors)
      gt_instances = InstanceData(bboxes=gt_bboxes, labels=gt_labels)
      gt_instances_ignore = InstanceData(bboxes=gt_bboxes_ignore)
  
      assign_result = center_region_assigner.assign(
          pred_instances,
          gt_instances,
          gt_instances_ignore=gt_instances_ignore,
      )
      self.assertEqual(len(assign_result.gt_inds), 0)
      self.assertTrue(tuple(assign_result.labels.shape) == (0,))
  
file_path: mmdetection/tests/test_models/test_task_modules/test_assigners/test_center_region_assigner.py
imports: from unittest import TestCase
  import torch
  from mmengine.structures import InstanceData
  from mmdet.models.task_modules.assigners import CenterRegionAssigner
label_desc: Use image node_id 5 for calling the TestCenterRegionAssigner obj's underlying member method code with example usage: obj.test_center_region_assigner_with_empty_boxes_and_ignore() without return types