Ensure that every test answer belongs to the test-corresponding question (#4181)

See [Cases-4181][] for motivation.

This was done by reviewing all uses of `Factory(:answer)`. This seems to cover the bulk of the CI failures caused by the underlying problem, but I haven't gone through all 100+ of them to verify that it covers them all.

When reviewing, please note the handful of occasions where more than just the test setup had to be modified. I'd appreciate review from the original authors of those tests to ensure that the tests were changed to test the wrong thing in these cases.

[Cases-4181]: https://code.bioinformatics.northwestern.edu/issues/issues/show/4181