Test cookie based authentication in server

[takethefake]

Currently, the cookie-based authentication isn't tested inside the server tests, because we don't have a real express.Response which contains the res.cookie function.

The current behavior to keep the tests running is because we added jest.fn in res.cookie in the GraphQLProvider- Context. We need a possibility to add jest.fn to res.cookie during the initialization of the test. Afterwards, we can check if res.cookie was called with the desired parameters.