make specs less coupled with implementation details

Gemfile

@@ -26,6 +26,8 @@ group :test do
 
   gem 'pry'
   gem 'pg_examiner', '~> 0.5.2'
+
+  gem 'timecop', '~> 0.9.10'
 end
 
 gemspec

spec/que/poller_spec.rb

@@ -283,8 +283,9 @@ def assert_poll(priorities:, locked:)
       result = poller.poll(priorities: { 500 => 7 }, held_locks: Set.new)
       assert_equal job_ids, result.map(&:id)
 
-      poller.instance_variable_set(:@next_poll_at, Time.now)
-      assert_equal true, poller.should_poll?
+      Timecop.freeze(Time.now + 30) do
+        assert_equal true, poller.should_poll?
+      end
     end
   end
 end

spec/spec_helper.rb

@@ -35,6 +35,10 @@
 require 'minitest/hooks'
 require 'minitest/profile'
 
+# "time travel" capabilities.
+require 'timecop'
+Timecop.safe_mode = true
+
 # Other support stuff.
 Dir['./spec/support/**/*.rb'].sort.each(&method(:require))