[#4420] Add the frequency field for Retainers to the Model and View.

test/unit/retainer_deliverable_test.rb

@@ -4,4 +4,9 @@ class RetainerDeliverableTest < ActiveSupport::TestCase
   should "be a subclass of HourlyDeliverable" do
     assert_equal HourlyDeliverable, RetainerDeliverable.superclass
   end
+
+  context "#frequency" do
+    should_allow_values_for(:frequency, nil, '', 'monthly', 'quarterly')
+    should_not_allow_values_for(:frequency, 'anything', 'else', 'weekly')
+  end
 end