testUnavailablePersistentFilesystem() {
    stubs.set(globalThis, 'requestFileSystem', null);
    stubs.set(globalThis, 'webkitRequestFileSystem', null);

    return googFs.getPersistent(2048).then(
        fail, /**
                 @suppress {strictMissingProperties} suppression added to
                 enable type checking
               */
        (e) => {
          assertEquals('File API unsupported', e.message);
        });
  }
@suppress {strictMissingProperties} suppression added to
                 enable type checking