Add active record's counter_cache support

lib/shoulda/matchers/active_record.rb

@@ -1,4 +1,5 @@
 require 'shoulda/matchers/active_record/association_matcher'
+require 'shoulda/matchers/active_record/association_matchers/counter_cache_matcher'
 require 'shoulda/matchers/active_record/association_matchers/order_matcher'
 require 'shoulda/matchers/active_record/association_matchers/through_matcher'
 require 'shoulda/matchers/active_record/association_matchers/dependent_matcher'

lib/shoulda/matchers/active_record/association_matcher.rb

@@ -98,6 +98,12 @@ def order(order)
           self
         end
 
+        def counter_cache(counter_cache = true)
+          counter_cache_matcher = AssociationMatchers::CounterCacheMatcher.new(counter_cache, name)
+          add_submatcher(counter_cache_matcher)
+          self
+        end
+
         def conditions(conditions)
           @options[:conditions] = conditions
           self

lib/shoulda/matchers/active_record/association_matchers/counter_cache_matcher.rb

@@ -0,0 +1,35 @@
+module Shoulda # :nodoc:
+  module Matchers
+    module ActiveRecord # :nodoc:
+      module AssociationMatchers
+        class CounterCacheMatcher
+          attr_accessor :missing_option
+
+          def initialize(counter_cache, name)
+            @counter_cache = counter_cache
+            @name = name
+            @missing_option = ''
+          end
+
+          def description
+            "counter_cache => #{counter_cache}"
+          end
+
+          def matches?(subject)
+            subject = ModelReflector.new(subject, name)
+
+            if subject.option_set_properly?(counter_cache, :counter_cache)
+              true
+            else
+              self.missing_option = "#{name} should have #{description}"
+              false
+            end
+          end
+
+          private
+          attr_accessor :counter_cache, :name
+        end
+      end
+    end
+  end
+end

spec/shoulda/matchers/active_record/association_matcher_spec.rb

@@ -46,6 +46,25 @@
       belonging_to_parent.should_not belong_to(:parent).dependent(:destroy)
     end
 
+    it 'accepts an association with a valid :counter_cache option' do
+      belonging_to_parent(:counter_cache => :attribute_count).
+        should belong_to(:parent).counter_cache(:attribute_count)
+    end
+
+    it 'defaults :counter_cache to true' do
+      belonging_to_parent(:counter_cache => true).
+        should belong_to(:parent).counter_cache
+    end
+
+    it 'rejects an association with a bad :counter_cache option' do
+      belonging_to_parent(:counter_cache => :attribute_count).
+        should_not belong_to(:parent).counter_cache(true)
+    end
+
+    it 'rejects an association that has no :counter_cache option' do
+      belonging_to_parent.should_not belong_to(:parent).counter_cache
+    end
+
     it 'accepts an association with a valid :conditions option' do
       define_model :parent, :adopter => :boolean
       define_model :child, :parent_id => :integer do