docstr: Test corner case where a network might predict no boxes.
code: def test_atss_assigner_with_empty_boxes(self):
      """Test corner case where a network might predict no boxes."""
      atss_assigner = ATSSAssigner(topk=9)
      priors = torch.empty((0, 4))
      gt_bboxes = torch.FloatTensor(
          [
              [0, 0, 10, 9],
              [0, 10, 10, 19],
          ]
      )
      gt_labels = torch.LongTensor([2, 3])
  
      pred_instances = InstanceData(priors=priors)
      gt_instances = InstanceData(bboxes=gt_bboxes, labels=gt_labels)
      num_level_bboxes = [0]
      assign_result = atss_assigner.assign(
          pred_instances, num_level_bboxes, gt_instances
      )
      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_atss_assigner.py
imports: from unittest import TestCase
  import torch
  from mmengine.structures import InstanceData
  from mmdet.models.task_modules.assigners import ATSSAssigner
label_desc: Use image node_id 4 for calling the TestATSSAssigner obj's underlying member method code with example usage: obj.test_atss_assigner_with_empty_boxes() without return types