[Skyy93]

According to the documentation and discussion about this feature some unit-tests are currently simple skipped: virtual filestem by Emscripten that's not fully POSIX compliant, no processes, no sockets, async only via the browser event loop (source: https://bugs.python.org/issue40280)

This would mean to me they simply do not work or only to an extend. As you can reading the virtual filesystem seems not fully compatible.