code: def test_set_heads(self):
      model = self.DummyTestModel()
      head = self.DummyTestHead()
      self.assertEqual(
          len(model.get_heads()),
          0,
          "heads should be empty before set_heads",
      )
      model.set_heads({"dummy_block2": [head]})
      input = torch.randn(1, 2)
      model(input)
      head_outputs = model.execute_heads()
      self.assertEqual(
          len(head_outputs), 1, "should have output for one head"
      )
  
      # remove all heads
      model.set_heads({})
      self.assertEqual(
          len(model.get_heads()), 0, "heads should be empty"
      )
  
      # try a non-existing module
      with self.assertRaises(Exception):
          model.set_heads({"unknown_block": [head]})
  
file_path: ClassyVision/test/models_classy_block_test.py
imports: import unittest
  import torch
  import torch.nn
  from classy_vision.heads import ClassyHead
  from classy_vision.models import ClassyModel, ClassyModelHeadExecutorWrapper, ClassyModelWrapper
label_desc: Use image node_id 6 for calling the TestClassyBlock obj's underlying member method code with example usage: obj.test_set_heads() without return types