docstr: Test if a `refs` points to a missing revision.
docstr_tok: ["Test","if","a","`","refs","`","points","to","a","missing","revision","."]
code: def test_ref_to_missing_revision(self) -> None:
      """Test if a `refs` points to a missing revision."""
      new_ref = self.repo_path / "refs" / "not_main"
      with new_ref.open("w") as f:
          f.write("revision_hash_that_does_not_exist")
  
      report = scan_cache_dir(self.cache_dir)
      self.assertEqual(len(report.repos), 0)  # Failed
  
      self.assertEqual(len(report.warnings), 1)
      self.assertEqual(
          str(report.warnings[0]),
          "Reference(s) refer to missing commit hashes: {'revision_hash_that_does_not_exist': {'not_main'}} "
          + f"({self.repo_path }).",
      )
  
imports: import os
  import tempfile
  import time
  import unittest
  from pathlib import Path
  from unittest.mock import Mock
  import pytest
  from huggingface_hub._snapshot_download import snapshot_download
  from huggingface_hub.commands.scan_cache import ScanCacheCommand
  from huggingface_hub.utils import DeleteCacheStrategy, HFCacheInfo, capture_output, scan_cache_dir
  from huggingface_hub.utils._cache_manager import CacheNotFound, _format_size, _format_timesince, _try_delete_path
  from .testing_constants import TOKEN
  from .testing_utils import rmtree_with_retry, with_production_testing, xfail_on_windows
label_desc: Use image node_id 7 for calling the TestCorruptedCacheUtils obj's underlying member method code with example usage: obj.test_ref_to_missing_revision() without return types