Avoid date changes during results tests.

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 consuldemocracy#2520 and consuldemocracy#2521.

[1] AyuntamientoMadrid#1342

spec/features/officing/results_spec.rb

@@ -1,8 +1,10 @@
 require 'rails_helper'
+require 'time_helper'
 
 feature 'Officing Results' do
 
   background do
+    freeze_time
     @poll_officer = create(:poll_officer)
     @officer_assignment = create(:poll_officer_assignment, :final, officer: @poll_officer)
     @poll = @officer_assignment.booth_assignment.poll
@@ -17,6 +19,10 @@
     login_as(@poll_officer.user)
   end
 
+  after do
+    travel_back
+  end
+
   scenario 'Only polls where user is officer for results are accessible' do
     regular_officer_assignment_1 = create(:poll_officer_assignment, officer: @poll_officer)
     regular_officer_assignment_2 = create(:poll_officer_assignment, officer: @poll_officer)

spec/time_helper.rb

@@ -0,0 +1,8 @@
+module ActiveSupport::Testing::TimeHelpers
+  # Copied from Rails 5.2. TODO: remove after migrating to Rails 5.
+  def freeze_time(&block)
+    travel_to Time.now, &block
+  end
+end
+
+include ActiveSupport::Testing::TimeHelpers