code: def test_builtin_head_as_custom(self):
      model_name = "bert-base-uncased"
      model_config = AutoConfig.from_pretrained(model_name)
      model_config.custom_heads = {"tag": CustomHead}
      model = AutoAdapterModel.from_pretrained(
          model_name, config=model_config
      )
      in_data = ids_tensor((1, 128), 1000)
  
      model.register_custom_head("classification", ClassificationHead)
      model.add_custom_head(
          head_type="classification",
          head_name="custom_head",
          num_labels=3,
          layers=2,
          activation_function="tanh",
      )
      model.eval()
      model.to(torch_device)
      output = model(in_data)
  
      self.assertEqual((1, 3), output[0].shape)
      self.assertEqual("custom_head", model.active_head)
  
file_path: adapters/tests/test_adapter_custom_head.py
imports: import tempfile
  import unittest
  import torch
  from adapters import AutoAdapterModel
  from adapters.heads import ClassificationHead, PredictionHead
  from transformers import AutoConfig
  from transformers.testing_utils import require_torch, torch_device
  from .test_adapter import ids_tensor
label_desc: Use image node_id 3 for calling the AdapterCustomHeadTest obj's underlying member method code with example usage: obj.test_builtin_head_as_custom() without return types