code: def test_mixed_stack(self):
      if (
          Stack in self.unsupported_blocks
          or Fuse in self.unsupported_blocks
      ):
          self.skipTest(
              "Stack or Fuse not supported by adapter config."
          )
  
      model = self.build_model()
      model.add_adapter_fusion(Fuse("a", "b"))
      model.to(torch_device)
  
      model.set_active_adapters(
          Stack("a", Split("c", "d", splits=64), Fuse("a", "b"))
      )
  
      self.training_pass(model)
  
imports: import unittest
  import torch
  import adapters
  from adapters import IA3Config, LoRAConfig, PrefixTuningConfig, SeqBnConfig
  from adapters.composition import Average, BatchSplit, Fuse, Parallel, Split, Stack, parse_composition
  from tests.test_adapter import ids_tensor
  from transformers import BertConfig, BertForSequenceClassification
  from transformers.testing_utils import require_torch, torch_device
label_desc: Use image node_id 9 for calling the AdapterCompositionTest obj's underlying member method code with example usage: obj.test_mixed_stack() without return types