+ Add inverse of matcher for active record association

NEWS.md

@@ -47,6 +47,8 @@
   `has_secure_password` defines #password= such that `nil` will be ignored,
   which interferes with how `validate_presence_of` works.
 
+* Add ability to test `belongs_to` associations defined with `:inverse_of`.
+
 # v 2.5.0
 
 * Fix Rails/Test::Unit integration to ensure that the test case classes we are

lib/shoulda/matchers/active_record.rb

@@ -1,5 +1,6 @@
 require 'shoulda/matchers/active_record/association_matcher'
 require 'shoulda/matchers/active_record/association_matchers/counter_cache_matcher'
+require 'shoulda/matchers/active_record/association_matchers/inverse_of_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

@@ -125,6 +125,13 @@ module Shoulda # :nodoc:
           self
         end
 
+        def inverse_of(inverse_of)
+          inverse_of_matcher =
+            AssociationMatchers::InverseOfMatcher.new(inverse_of, name)
+          add_submatcher(inverse_of_matcher)
+          self
+        end
+
         def source(source)
           source_matcher = AssociationMatchers::SourceMatcher.new(source, name)
           add_submatcher(source_matcher)

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

@@ -0,0 +1,40 @@
+module Shoulda # :nodoc:
+  module Matchers
+    module ActiveRecord # :nodoc:
+      module AssociationMatchers
+        class InverseOfMatcher
+          attr_accessor :missing_option
+
+          def initialize(inverse_of, name)
+            @inverse_of = inverse_of
+            @name = name
+            @missing_option = ''
+          end
+
+          def description
+            "inverse_of => #{inverse_of}"
+          end
+
+          def matches?(subject)
+            self.subject = ModelReflector.new(subject, name)
+
+            if option_verifier.correct_for_string?(:inverse_of, inverse_of)
+              true
+            else
+              self.missing_option = "#{name} should have #{description}"
+              false
+            end
+          end
+
+          private
+
+          attr_accessor :subject, :inverse_of, :name
+
+          def option_verifier
+            @option_verifier ||= OptionVerifier.new(subject)
+          end
+        end
+      end
+    end
+  end
+end

spec/shoulda/matchers/active_record/association_matcher_spec.rb

@@ -66,6 +66,21 @@ describe Shoulda::Matchers::ActiveRecord::AssociationMatcher do
       expect(belonging_to_parent).not_to belong_to(:parent).counter_cache
     end
 
+    it 'accepts an association with a valid :inverse_of option' do
+      expect(belonging_to_parent(inverse_of: :children))
+        .to belong_to(:parent).inverse_of(:children)
+    end
+
+    it 'rejects an association with a bad :inverse_of option' do
+      expect(belonging_to_parent(inverse_of: :other_children))
+        .not_to belong_to(:parent).inverse_of(:children)
+    end
+
+    it 'rejects an association that has no :inverse_of option' do
+      expect(belonging_to_parent)
+        .not_to belong_to(:parent).inverse_of(:children)
+    end
+
     it 'accepts an association with a valid :conditions option' do
       define_model :parent, adopter: :boolean
       define_model(:child, parent_id: :integer).tap do |model|