code: def test_get_filesystem_custom_filesystem():
      _DUMMY_PRFEIX = "dummy"
  
      class DummyFileSystem(LocalFileSystem):
          ...
  
      fsspec.register_implementation(
          _DUMMY_PRFEIX, DummyFileSystem, clobber=True
      )
      output_file = os.path.join(
          f"{_DUMMY_PRFEIX}://", "tmpdir/tmp_file"
      )
      assert isinstance(get_filesystem(output_file), DummyFileSystem)
  
file_path: pytorch-lightning/tests/tests_fabric/utilities/test_cloud_io.py
imports: import os
  import fsspec
  from fsspec.implementations.local import LocalFileSystem
  from fsspec.spec import AbstractFileSystem
  from lightning.fabric.utilities.cloud_io import _is_dir, get_filesystem
label_desc: Use image node_id 1 for calling a global function with example usage: test_get_filesystem_custom_filesystem() without return types