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.
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.
As explained by @iagirre with pinpoint accuracy [1]:
"If the officer_assignments are created at 23:59:59 and the rest of the
test is executed after 00:00:00, the dates for the objects and the
`Date.current` (used to check if there are any shifts today) won't be
the same, because the shift will be for, lets say, 07/03/2018 and
`Date.current` will be 08/03/2018, so, there are no shifts."
Freezing time avoids this issue.
Related to issues #2520 and #2521.
[1] https://github.com/AyuntamientoMadrid/consul/pull/1342
