Today I shipped vfsStream 0.5.0 which brings a new feature thanks to the efforts of Benoit Aubuchon: vfsStream now supports the rename() functionality which allows you to write test cases using vfsStream for methods that rename files. Another patch of him was to change the stat() call to respect the STREAM_URL_STAT_QUIET flag.
One more new feature is the added support for . as current directory alias so that vfs://foo/. resolves to vfs://foo - this allows to use file_exists($dir . '/.') as workaround for the failing is_executable() call on directories, as described in the comments to the is_executable() documentation in the PHP manual. Of course this raises the question if vfsStream will support .. as well - if somebody takes the time to create a patch I will incorporate this. I did not look into this issue further, but I guess it might involve recursion and a more advanced parsing of the vfs URL to make it work properly, as there might be cases like vfs://foo/bar/baz/../../dummy.