diff --git a/actionpack/lib/action_dispatch/http/request.rb b/actionpack/lib/action_dispatch/http/request.rb
index b0ed681623cbd..30566f0d79a37 100644
--- a/actionpack/lib/action_dispatch/http/request.rb
+++ b/actionpack/lib/action_dispatch/http/request.rb
@@ -331,6 +331,8 @@ def body_stream #:nodoc:
 
     # TODO This should be broken apart into AD::Request::Session and probably
     # be included by the session middleware.
+    # もしかしたらコメント削除してしまっていいのかも？
+    # [Just reading flash messages should not create a session if one does n… · rails/rails@a12b76b](https://github.com/rails/rails/commit/a12b76b09e98493c1e4aee147416ae5999402298)
     def reset_session
       if session && session.respond_to?(:destroy)
         session.destroy
diff --git a/actionpack/test/controller/force_ssl_test.rb b/actionpack/test/controller/force_ssl_test.rb
index 03a9c9ae78220..ef3eec20988ad 100644
--- a/actionpack/test/controller/force_ssl_test.rb
+++ b/actionpack/test/controller/force_ssl_test.rb
@@ -230,6 +230,7 @@ def test_cheeseburger_redirects_to_https
     assert_equal "http://test.host/force_ssl_flash/cheeseburger", redirect_to_url
 
     # FIXME: AC::TestCase#build_request_uri doesn't build a new uri if PATH_INFO exists
+    # AC::TestCase#build_request_uri がないので一回消して通るか確かめてみたい
     @request.env.delete('PATH_INFO')
 
     get :cheeseburger
@@ -237,6 +238,7 @@ def test_cheeseburger_redirects_to_https
     assert_equal "https://test.host/force_ssl_flash/cheeseburger", redirect_to_url
 
     # FIXME: AC::TestCase#build_request_uri doesn't build a new uri if PATH_INFO exists
+    # AC::TestCase#build_request_uri がないので一回消して通るか確かめてみたい
     @request.env.delete('PATH_INFO')
 
     get :use_flash
diff --git a/actionview/test/activerecord/polymorphic_routes_test.rb b/actionview/test/activerecord/polymorphic_routes_test.rb
index 34b2698c7f321..d6ce2c94f804b 100644
--- a/actionview/test/activerecord/polymorphic_routes_test.rb
+++ b/actionview/test/activerecord/polymorphic_routes_test.rb
@@ -88,6 +88,8 @@ def test_string
     with_test_routes do
       # FIXME: why are these different? Symbol case passes through to
       # `polymorphic_url`, but the String case doesn't.
+      # これ単純に消しても問題ないコメントなのかも？
+      # [test for inconsistency between String and Symbol url_for handling · rails/rails@37d4415](https://github.com/rails/rails/commit/37d4415a7b433fcb987b1c6a5b51bf2d8efc5d5e)
       assert_equal "http://example.com/projects", polymorphic_url("projects")
       assert_equal "projects", url_for("projects")
     end
diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index eef2d29d02055..0c237445f4e28 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -887,6 +887,7 @@ def test_bignum
   end
 
   # TODO: extend defaults tests to other databases!
+  # これ mysql 版いけるのでは？
   if current_adapter?(:PostgreSQLAdapter)
     def test_default
       with_timezone_config default: :local do
diff --git a/activerecord/test/cases/finder_test.rb b/activerecord/test/cases/finder_test.rb
index f03df2d99e8d1..e9f91adea93d4 100644
--- a/activerecord/test/cases/finder_test.rb
+++ b/activerecord/test/cases/finder_test.rb
@@ -498,6 +498,7 @@ def test_second_to_last
 
     #test with limit
     # assert_equal nil, Topic.limit(1).second # TODO: currently failing
+    # 今日の master コンソール上で試したら nil 帰ってきたのでもう動くのではという気がする
     assert_equal nil, Topic.limit(1).second_to_last
   end
 
@@ -527,8 +528,10 @@ def test_third_to_last
 
     # test with limit
     # assert_equal nil, Topic.limit(1).third # TODO: currently failing
+    # 今日の master コンソール上で試したら nil 帰ってきたのでもう動くのではという気がする
     assert_equal nil, Topic.limit(1).third_to_last
     # assert_equal nil, Topic.limit(2).third # TODO: currently failing
+    # 今日の master コンソール上で試したら nil 帰ってきたのでもう動くのではという気がする
     assert_equal nil, Topic.limit(2).third_to_last
   end
 
diff --git a/activerecord/test/cases/helper.rb b/activerecord/test/cases/helper.rb
index d2fdf03e9d002..42bf5f7bf61f0 100644
--- a/activerecord/test/cases/helper.rb
+++ b/activerecord/test/cases/helper.rb
@@ -14,7 +14,7 @@
 require 'support/connection'
 
 # TODO: Move all these random hacks into the ARTest namespace and into the support/ dir
-
+# ロジック移動させるだけで済むのかもしれない
 Thread.abort_on_exception = true
 
 # Show backtraces for deprecated behavior for quicker cleanup.
@@ -202,3 +202,5 @@ def in_time_zone(zone)
 end
 
 require 'mocha/setup' # FIXME: stop using mocha
+# 根気があれば直せるのでは
+# ひたすら minitest のモックの記法に置換していくだけでいける？
diff --git a/activerecord/test/cases/validations/i18n_validation_test.rb b/activerecord/test/cases/validations/i18n_validation_test.rb
index b8307d6665dac..11138d766a513 100644
--- a/activerecord/test/cases/validations/i18n_validation_test.rb
+++ b/activerecord/test/cases/validations/i18n_validation_test.rb
@@ -45,6 +45,8 @@ def replied_topic
     # TODO Add :on case, but below doesn't work, because then the validation isn't run for some reason
     #      even when using .save instead .valid?
     # [ "given on condition",     {on: :save},                {}]
+    # とりあえず、ある程度泥臭く書けば on はサポートできそう
+    # そこから綺麗に書ける方法を見つけられればマージされるのでは？
   ]
 
   COMMON_CASES.each do |name, validation_options, generate_message_options|