Follow up to #1535

- The removed classes and modules were added back with deprecation
  warning and deprecation test were added for them.
- One test was renamed because it contained `__`.
- Some tests were refactored.
- The ActiveModelSerializers::Deserialization module is now called
  Adapter instead of ActiveModelSerializers::Adapter.
- The changelog was added for #1535

test/adapter/json_api/relationships_test.rb

@@ -0,0 +1,192 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    module Adapter
+      class JsonApi
+        class RelationshipTest < ActiveSupport::TestCase
+          RelationshipAuthor = Class.new(::Model)
+          class RelationshipAuthorSerializer < ActiveModel::Serializer
+            has_one :bio do
+              link :self, '//example.com/link_author/relationships/bio'
+            end
+
+            has_one :profile do
+              link :related do
+                "//example.com/profiles/#{object.profile.id}"
+              end
+            end
+
+            has_many :locations do
+              link :related do
+                ids = object.locations.map(&:id).join(',')
+                href "//example.com/locations/#{ids}"
+              end
+            end
+
+            has_many :posts do
+              link :related do
+                ids = object.posts.map(&:id).join(',')
+                href "//example.com/posts/#{ids}"
+                meta ids: ids
+              end
+            end
+
+            has_many :comments do
+              link :self do
+                meta ids: [1]
+              end
+            end
+
+            has_many :roles do
+              meta count: object.posts.count
+            end
+
+            has_one :blog do
+              link :self, '//example.com/link_author/relationships/blog'
+              include_data false
+            end
+
+            belongs_to :reviewer do
+              meta name: 'Dan Brown'
+              include_data true
+            end
+
+            has_many :likes do
+              link :related do
+                ids = object.likes.map(&:id).join(',')
+                href "//example.com/likes/#{ids}"
+                meta ids: ids
+              end
+              meta liked: object.likes.any?
+            end
+          end
+
+          def setup
+            @post = Post.new(id: 1337, comments: [], author: nil)
+            @blog = Blog.new(id: 1337, name: 'extra')
+            @bio = Bio.new(id: 1337)
+            @like = Like.new(id: 1337)
+            @role = Role.new(id: 1337)
+            @profile = Profile.new(id: 1337)
+            @location = Location.new(id: 1337)
+            @reviewer = Author.new(id: 1337)
+            @comment = Comment.new(id: 1337)
+            @author = RelationshipAuthor.new(
+              id: 1337,
+              posts: [@post],
+              blog: @blog,
+              reviewer: @reviewer,
+              bio: @bio,
+              likes: [@like],
+              roles: [@role],
+              locations: [@location],
+              profile: @profile,
+              comments: [@comment]
+            )
+          end
+
+          def test_relationship_simple_link
+            expected = {
+              data: {
+                id: '1337',
+                type: 'bios'
+              },
+              links: {
+                self: '//example.com/link_author/relationships/bio'
+              }
+            }
+            assert_relationship(:bio, expected)
+          end
+
+          def test_relationship_block_link
+            expected = {
+              data: { id: '1337', type: 'profiles' },
+              links: { related: '//example.com/profiles/1337' }
+            }
+            assert_relationship(:profile, expected)
+          end
+
+          def test_relationship_block_link_href
+            expected = {
+              data: [{ id: '1337', type: 'locations' }],
+              links: {
+                related: { href: '//example.com/locations/1337' }
+              }
+            }
+            assert_relationship(:locations, expected)
+          end
+
+          def test_relationship_block_link_href_and_meta
+            expected = {
+              data: [{ id: '1337', type: 'posts' }],
+              links: {
+                related: {
+                  href: '//example.com/posts/1337',
+                  meta: { ids: '1337' }
+                }
+              }
+            }
+            assert_relationship(:posts, expected)
+          end
+
+          def test_relationship_block_link_meta
+            expected = {
+              data: [{ id: '1337', type: 'comments' }],
+              links: {
+                self: {
+                  meta: { ids: [1] }
+                }
+              }
+            }
+            assert_relationship(:comments, expected)
+          end
+
+          def test_relationship_meta
+            expected = {
+              data: [{ id: '1337', type: 'roles' }],
+              meta: { count: 1 }
+            }
+            assert_relationship(:roles, expected)
+          end
+
+          def test_relationship_not_including_data
+            expected = {
+              links: { self: '//example.com/link_author/relationships/blog' }
+            }
+            assert_relationship(:blog, expected)
+          end
+
+          def test_relationship_including_data_explicit
+            expected = {
+              data: { id: '1337', type: 'authors' },
+              meta: { name: 'Dan Brown' }
+            }
+            assert_relationship(:reviewer, expected)
+          end
+
+          def test_relationship_with_everything
+            expected = {
+              data: [{ id: '1337', type: 'likes' }],
+              links: {
+                related: {
+                  href: '//example.com/likes/1337',
+                  meta: { ids: '1337' }
+                }
+              },
+              meta: { liked: true }
+            }
+            assert_relationship(:likes, expected)
+          end
+
+          private
+
+          def assert_relationship(relationship_name, expected)
+            hash = serializable(@author, adapter: :json_api).serializable_hash
+            assert_equal(expected, hash[:data][:relationships][relationship_name])
+          end
+        end
+      end
+    end
+  end
+end