Note we usually cannot make it simple because officer assignments are
usually assigned to both a poll and a booth, and on a certain date.
However, in the few cases where the booth nor the date don't matter, we
can make the code a bit easier to read.
While it could be argued we're hiding the real way we've defined
associations in our models, the tests are so much easier to read when we
don't have so many lines just creating data.
Furthermore, developers who care about vertically aligning the code will
be glad to see some variables disrupting this alignment are now gone.
The `type: :feature` is automatically detected by RSpec because these
tests are inside the `spec/features` folder. Using `feature` re-adds a
`type: :feature` to these files, which will result in a conflict when we
upgrade to Rails 5.1's system tests.
Because of this change, we also need to change `background` to `before`
or else these tests will fail.
