Encapsulate the concept of staleness into its own class

Extract it from a single helper method and wrap it in a method object.
This lets us add tests around it and then (later) split the domain
concerns from the view concerns.

lib/staleness.rb

@@ -0,0 +1,18 @@
+require 'active_support/all'
+
+class Staleness
+  def self.days_stale(item, current_user)
+    if item.due || item.completed?
+      return ""
+    elsif item.created_at < current_user.time - (current_user.prefs.staleness_starts * 3).days
+      return " stale_l3"
+    elsif item.created_at < current_user.time - (current_user.prefs.staleness_starts * 2).days
+      return " stale_l2"
+    elsif item.created_at < current_user.time - (current_user.prefs.staleness_starts).days
+      return " stale_l1"
+    else
+      return ""
+    end
+  end
+end
+

test/unit/staleness_test.rb

@@ -0,0 +1,71 @@
+require_relative '../minimal_test_helper'
+require_relative '../../lib/staleness'
+
+FakeUser = Struct.new(:time, :prefs)
+FakePrefs = Struct.new(:staleness_starts)
+FakeTask = Struct.new(:due, :completed, :created_at) do
+  def completed?
+    self.completed
+  end
+end
+
+class StalenessTest < Test::Unit::TestCase
+
+  def now
+    @now ||= Time.utc(2013, 2, 28, 0, 0, 0)
+  end
+
+  def day0
+    @day0 ||= Time.utc(2013, 2, 27, 0, 0, 0)
+  end
+
+  def day24
+    @day24 ||= Time.utc(2013, 2, 4, 0, 0, 0)
+  end
+
+  def day16
+    @day16 ||= Time.utc(2013, 2, 12, 0, 0, 0)
+  end
+
+  def day8
+    @day8 ||= Time.utc(2013, 2, 20, 0, 0, 0)
+  end
+
+  def fake_prefs
+    @fake_prefs ||= FakePrefs.new(7)
+  end
+
+  def setup
+    @current_user = FakeUser.new(now, fake_prefs)
+  end
+
+  def test_item_with_due_date_is_not_stale_ever
+    todo = FakeTask.new(day24, false, now)
+    assert_equal "", Staleness.days_stale(todo, @current_user)
+  end
+
+  def test_complete_item_is_not_stale
+    todo = FakeTask.new(day16, true, day24)
+    assert_equal "", Staleness.days_stale(todo, @current_user)
+  end
+
+  def test_young_item_is_not_stale
+    todo = FakeTask.new(nil, false, now)
+    assert_equal "", Staleness.days_stale(todo, @current_user)
+  end
+
+  def test_staleness_level_one
+    todo = FakeTask.new(nil, false, day8)
+    assert_equal " stale_l1", Staleness.days_stale(todo, @current_user)
+  end
+
+  def test_staleness_level_two
+    todo = FakeTask.new(nil, false, day16)
+    assert_equal " stale_l2", Staleness.days_stale(todo, @current_user)
+  end
+
+  def test_staleness_level_three
+    todo = FakeTask.new(nil, false, day24)
+    assert_equal " stale_l3", Staleness.days_stale(todo, @current_user)
+  end
+end