Add test for visited/successful state setting

With #100, for every logged in user we create a state for each challenge. Test that this is done correctly in a positive and negative way.
- positive: each visited challenge gets the `visited` state
- negative: each non-visited challenge does not get the `visited` tag

Further check the same for each successfully/not-successfully tried session

This can be done after [#101](https://github.com/CloseChoice/dataframetrainer/issues/101) is fixed