code: def test_concatenate(batch):
      b = batch
      files = []
      for _ in range(10):
          j = b.new_job()
          j.command(f"touch {j.ofile}")
          files.append(j.ofile)
      concatenate(b, files, branching_factor=2)
      assert len(b._jobs) == 10 + (5 + 3 + 2 + 1)
      b.run()
  
imports: from typing import AsyncIterator
  import os
  import pytest
  import subprocess
  import tempfile
  from hailtop import pip_version
  from hailtop.batch import Batch, LocalBackend, ResourceGroup
  from hailtop.batch.resource import JobResourceFile
  from hailtop.batch.utils import concatenate
label_desc: Use image node_id 26 for calling a global function with example usage: test_concatenate(batch) without return types