Game lifecycle tests and utils.js tests

[Soreine]

Tests currently fail with

  1) Game lifecycle Given an authenticated user should be able to create a new game without any password:
     Uncaught SyntaxError: Unexpected token T
      at Object.parse (native)
      at IncomingMessage.<anonymous> (utils.js:40:34)
      at endReadableNT (_stream_readable.js:905:12)

This error happens at the last middleware level:

// backend/src/main.js:14
app.use((err, req, res, next) => { // eslint-disable-line no-unused-vars
    console.log(err)
    res.status(err.code)
    res.json(err) // fails
})

[Soreine]

:sunrise: