Add a test checking that problem addition in unstructured exams works
Maybe also add a check that page numbers correspond to problems, etc
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The following discussion from !309 should be addressed:
- [ ] @anton-akhmerov started a [discussion](https://gitlab.kwant-project.org/zesje/zesje/-/merge_requests/309#note_44962):
> Can you please add a test as well?
issue