Use the same system to freeze time in all specs

This required changing the `voted_before_sign_in` slightly in order to
change what the method returns if the user signed in and voted at the
exact same microsecond.

It doesn't affect production code because it would be impossible for the
user to do both things at the same time.

As a side effect, the method now returns what the method name suggests.
Before this change, the correct method name would have been
`voted_before_or_at_the_same_time_of_sign_in`.

As a less desirable side effect, in the tests now we need to make sure
at least one second passes between the moment a user votes and the
moment a user signs in again. One microsecond wouldn't work because
the method `travel_to` automatically sets microseconds to zero in order
to avoid rounding issues.

app/helpers/polls_helper.rb

@@ -46,7 +46,7 @@ module PollsHelper
   end
 
   def voted_before_sign_in(question)
-    question.answers.where(author: current_user).any? { |vote| current_user.current_sign_in_at >= vote.updated_at }
+    question.answers.where(author: current_user).any? { |vote| current_user.current_sign_in_at > vote.updated_at }
   end
 
 end

spec/features/polls/polls_spec.rb

@@ -387,18 +387,12 @@ feature 'Polls' do
     end
   end
 
-  context 'Booth & Website' do
+  context 'Booth & Website', :with_frozen_time do
 
-    let(:poll) { create(:poll, summary: "Summary", description: "Description", starts_at: '2017-12-01', ends_at: '2018-02-01') }
+    let(:poll) { create(:poll, summary: "Summary", description: "Description") }
     let(:booth) { create(:poll_booth) }
     let(:officer) { create(:poll_officer) }
 
-    before do
-      allow(Date).to receive(:current).and_return Date.new(2018,1,1)
-      allow(Date).to receive(:today).and_return Date.new(2018,1,1)
-      allow(Time).to receive(:current).and_return Time.zone.parse("2018-01-01 12:00:00")
-    end
-
     scenario 'Already voted on booth cannot vote on website', :js do
 
       create(:poll_shift, officer: officer, booth: booth, date: Date.current, task: :vote_collection)

spec/features/polls/voter_spec.rb

@@ -2,7 +2,7 @@ require 'rails_helper'
 
 feature "Voter" do
 
-  context "Origin" do
+  context "Origin", :with_frozen_time do
 
     let(:poll) { create(:poll, :current) }
     let(:question) { create(:poll_question, poll: poll) }
@@ -125,12 +125,18 @@ feature "Voter" do
 
         click_link "Sign out"
 
-        login_as user
-        visit poll_path(poll)
+        # Time needs to pass between the moment we vote and the moment
+        # we log in; otherwise the link to vote won't be available.
+        # It's safe to advance one second because this test isn't
+        # affected by possible date changes.
+        travel 1.second do
+          login_as user
+          visit poll_path(poll)
 
-        within("#poll_question_#{question.id}_answers") do
-          expect(page).to have_link(answer_yes.title)
-          expect(page).to have_link(answer_no.title)
+          within("#poll_question_#{question.id}_answers") do
+            expect(page).to have_link(answer_yes.title)
+            expect(page).to have_link(answer_no.title)
+          end
         end
       end
     end