1 files changed, 127 insertions, 0 deletions
diff --git a/activerecord/test/cases/attribute_decorators_test.rb b/activerecord/test/cases/attribute_decorators_test.rb
new file mode 100644
index 0000000000..42eca233ce
--- /dev/null
+++ b/activerecord/test/cases/attribute_decorators_test.rb
@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+module ActiveRecord
+  class AttributeDecoratorsTest < ActiveRecord::TestCase
+    class Model < ActiveRecord::Base
+      self.table_name = "attribute_decorators_model"
+    end
+
+    class StringDecorator < SimpleDelegator
+      def initialize(delegate, decoration = "decorated!")
+        @decoration = decoration
+        super(delegate)
+      end
+
+      def cast(value)
+        "#{super} #{@decoration}"
+      end
+
+      alias deserialize cast
+    end
+
+    setup do
+      @connection = ActiveRecord::Base.connection
+      @connection.create_table :attribute_decorators_model, force: true do |t|
+        t.string :a_string
+      end
+    end
+
+    teardown do
+      return unless @connection
+      @connection.drop_table "attribute_decorators_model", if_exists: true
+      Model.attribute_type_decorations.clear
+      Model.reset_column_information
+    end
+
+    test "attributes can be decorated" do
+      model = Model.new(a_string: "Hello")
+      assert_equal "Hello", model.a_string
+
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+
+      model = Model.new(a_string: "Hello")
+      assert_equal "Hello decorated!", model.a_string
+    end
+
+    test "decoration does not eagerly load existing columns" do
+      Model.reset_column_information
+      assert_no_queries do
+        Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+      end
+    end
+
+    test "undecorated columns are not touched" do
+      Model.attribute :another_string, :string, default: "something or other"
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+
+      assert_equal "something or other", Model.new.another_string
+    end
+
+    test "decorators can be chained" do
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+      Model.decorate_attribute_type(:a_string, :other) { |t| StringDecorator.new(t) }
+
+      model = Model.new(a_string: "Hello!")
+
+      assert_equal "Hello! decorated! decorated!", model.a_string
+    end
+
+    test "decoration of the same type multiple times is idempotent" do
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+
+      model = Model.new(a_string: "Hello")
+      assert_equal "Hello decorated!", model.a_string
+    end
+
+    test "decorations occur in order of declaration" do
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+      Model.decorate_attribute_type(:a_string, :other) do |type|
+        StringDecorator.new(type, "decorated again!")
+      end
+
+      model = Model.new(a_string: "Hello!")
+
+      assert_equal "Hello! decorated! decorated again!", model.a_string
+    end
+
+    test "decorating attributes does not modify parent classes" do
+      Model.attribute :another_string, :string, default: "whatever"
+      Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
+      child_class = Class.new(Model)
+      child_class.decorate_attribute_type(:another_string, :test) { |t| StringDecorator.new(t) }
+      child_class.decorate_attribute_type(:a_string, :other) { |t| StringDecorator.new(t) }
+
+      model = Model.new(a_string: "Hello!")
+      child = child_class.new(a_string: "Hello!")
+
+      assert_equal "Hello! decorated!", model.a_string
+      assert_equal "whatever", model.another_string
+      assert_equal "Hello! decorated! decorated!", child.a_string
+      assert_equal "whatever decorated!", child.another_string
+    end
+
+    class Multiplier < SimpleDelegator
+      def cast(value)
+        return if value.nil?
+        value * 2
+      end
+      alias deserialize cast
+    end
+
+    test "decorating with a proc" do
+      Model.attribute :an_int, :integer
+      type_is_integer = proc { |_, type| type.type == :integer }
+      Model.decorate_matching_attribute_types type_is_integer, :multiplier do |type|
+        Multiplier.new(type)
+      end
+
+      model = Model.new(a_string: "whatever", an_int: 1)
+
+      assert_equal "whatever", model.a_string
+      assert_equal 2, model.an_int
+    end
+  end
+end