Extract `FakeKlass` in `relation_test.rb` and `relation/mutation_test.rb`

`FakeKlass` in `relation_test.rb` and `relation/mutation_test.rb` are
almost the same.

activerecord/test/cases/relation/mutation_test.rb

@@ -3,39 +3,6 @@
 
 module ActiveRecord
   class RelationMutationTest < ActiveRecord::TestCase
-    FakeKlass = Struct.new(:table_name, :name) do
-      extend ActiveRecord::Delegation::DelegateCache
-      inherited self
-
-      def connection
-        Post.connection
-      end
-
-      def relation_delegate_class(klass)
-        self.class.relation_delegate_class(klass)
-      end
-
-      def attribute_alias?(name)
-        false
-      end
-
-      def sanitize_sql(sql)
-        sql
-      end
-
-      def sanitize_sql_for_order(sql)
-        sql
-      end
-
-      def arel_attribute(name, table)
-        table[name]
-      end
-    end
-
-    def relation
-      @relation ||= Relation.new FakeKlass.new("posts"), Post.arel_table, Post.predicate_builder
-    end
-
     (Relation::MULTI_VALUE_METHODS - [:references, :extending, :order, :unscope, :select]).each do |method|
       test "##{method}!" do
         assert relation.public_send("#{method}!", :foo).equal?(relation)
@@ -167,5 +134,10 @@ def relation
       relation.skip_query_cache!
       assert relation.skip_query_cache_value
     end
+
+    private
+      def relation
+        @relation ||= Relation.new(FakeKlass, Post.arel_table, Post.predicate_builder)
+      end
   end
 end

activerecord/test/cases/relation_test.rb

@@ -8,24 +8,6 @@ module ActiveRecord
   class RelationTest < ActiveRecord::TestCase
     fixtures :posts, :comments, :authors, :author_addresses, :ratings
 
-    FakeKlass = Struct.new(:table_name, :name) do
-      extend ActiveRecord::Delegation::DelegateCache
-
-      inherited self
-
-      def self.connection
-        Post.connection
-      end
-
-      def self.table_name
-        "fake_table"
-      end
-
-      def self.sanitize_sql_for_order(sql)
-        sql
-      end
-    end
-
     def test_construction
       relation = Relation.new(FakeKlass, :b, nil)
       assert_equal FakeKlass, relation.klass
@@ -90,7 +72,7 @@ def test_tree_is_not_traversed
     end
 
     def test_table_name_delegates_to_klass
-      relation = Relation.new(FakeKlass.new("posts"), :b, Post.predicate_builder)
+      relation = Relation.new(FakeKlass, :b, Post.predicate_builder)
       assert_equal "posts", relation.table_name
     end
 

activerecord/test/models/post.rb

@@ -276,3 +276,35 @@ class ConditionalStiPost < Post
 
 class SubConditionalStiPost < ConditionalStiPost
 end
+
+class FakeKlass
+  extend ActiveRecord::Delegation::DelegateCache
+
+  inherited self
+
+  class << self
+    def connection
+      Post.connection
+    end
+
+    def table_name
+      "posts"
+    end
+
+    def attribute_alias?(name)
+      false
+    end
+
+    def sanitize_sql(sql)
+      sql
+    end
+
+    def sanitize_sql_for_order(sql)
+      sql
+    end
+
+    def arel_attribute(name, table)
+      table[name]
+    end
+  end
+end