update specs; add new specs to test for reported bug related to AND query in referenced table

spec/schema.rb

@@ -27,6 +27,7 @@ ActiveRecord::Schema.define do
 
   create_table :tags, force: true do |t|
     t.string :value
+    t.string :custom_attribute
     t.references :category, index: true
     t.references :taggable, polymorphic: true, index: true
     t.timestamps null: false
@@ -34,6 +35,7 @@ ActiveRecord::Schema.define do
 
   create_table :categories, force: true do |t|
     t.string :name
+    t.references :categoriable, polymorphic: true, index: true
     t.timestamps null: false
   end