code: def test_filenames_from_a_directory():
      """Verify that filenames_from walks a directory."""
      filenames = set(
          _filenames_from(_normpath("a/b/"), predicate=_noop)
      )
      # should include all files
      expected = _normpaths(("a/b/c.py", "a/b/d.py", "a/b/e/f.py"))
      assert filenames == expected
  
imports: from __future__ import annotations
  import os.path
  import pytest
  from flake8 import utils
  from flake8.discover_files import _filenames_from
  from flake8.discover_files import expand_paths
label_desc: Use image node_id 5 for calling a global function with example usage: test_filenames_from_a_directory() without return types