diff --git a/Gemfile b/Gemfile
index 2d300d3c..b6eb8a9e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -96,8 +96,6 @@ group :development, :test do
   # Call 'byebug' anywhere in the code to stop execution and get a debugger console
   gem 'byebug'
 
-  gem 'minitest-reporters'
-
   gem 'guard'
   gem 'guard-minitest'
 
@@ -111,6 +109,8 @@ end
 group :test do
   gem 'test-unit-rails'
 
+  gem 'database_cleaner-active_record'
+
   gem 'rake'
   gem 'rubocop'
   gem 'rubocop-rails'
diff --git a/Gemfile.lock b/Gemfile.lock
index 83ecad70..e3c61f9c 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -71,7 +71,6 @@ GEM
       zeitwerk (~> 2.3)
     addressable (2.8.0)
       public_suffix (>= 2.0.2, < 5.0)
-    ansi (1.5.0)
     ast (2.4.2)
     autoprefixer-rails (10.2.5.1)
       execjs (> 0)
@@ -98,6 +97,10 @@ GEM
     concurrent-ruby (1.1.9)
     connection_pool (2.2.5)
     crass (1.0.6)
+    database_cleaner-active_record (2.0.1)
+      activerecord (>= 5.a)
+      database_cleaner-core (~> 2.0.0)
+    database_cleaner-core (2.0.1)
     docile (1.4.0)
     erubi (1.10.0)
     execjs (2.8.1)
@@ -184,11 +187,6 @@ GEM
     method_source (1.0.0)
     mini_mime (1.1.0)
     minitest (5.14.4)
-    minitest-reporters (1.4.3)
-      ansi
-      builder
-      minitest (>= 5.0)
-      ruby-progressbar
     msgpack (1.4.2)
     multi_json (1.15.0)
     multi_xml (0.6.0)
@@ -196,6 +194,8 @@ GEM
     mysql2 (0.5.3)
     nenv (0.3.0)
     nio4r (2.5.7)
+    nokogiri (1.11.7-x86_64-darwin)
+      racc (~> 1.4)
     nokogiri (1.11.7-x86_64-linux)
       racc (~> 1.4)
     notiffany (0.1.3)
@@ -383,6 +383,7 @@ GEM
     zeitwerk (2.4.2)
 
 PLATFORMS
+  x86_64-darwin-20
   x86_64-linux
 
 DEPENDENCIES
@@ -392,6 +393,7 @@ DEPENDENCIES
   byebug
   capybara (>= 3.26)
   cfnv
+  database_cleaner-active_record
   factory_bot_rails
   friendly_id
   guard
@@ -403,7 +405,6 @@ DEPENDENCIES
   lumberjack
   mcinch
   meta-tags
-  minitest-reporters
   mysql2 (~> 0.5)
   pry-rails
   puma
diff --git a/app/controllers/admin/archived_conversation_messages_controller.rb b/app/controllers/admin/archived_conversation_messages_controller.rb
index 226c02dc..8ead7786 100644
--- a/app/controllers/admin/archived_conversation_messages_controller.rb
+++ b/app/controllers/admin/archived_conversation_messages_controller.rb
@@ -21,7 +21,8 @@ def show
   def create
     archiver = ConversationMessageArchiver.new
 
-    if am = archiver.archive!(archived_conversation_message_params_for_create)
+    am = archiver.archive!(archived_conversation_message_params_for_create)
+    if am
       flash[:success] = t('views.flash.added_archived_conversation_message')
       redirect_to(admin_archived_conversation_message_path(am.id))
     else
@@ -49,7 +50,8 @@ def update
   def destroy
     archiver = ConversationMessageArchiver.new
 
-    if cm = archiver.reconstitute!(params[:id])
+    cm = archiver.reconstitute!(params[:id].to_i)
+    if cm
       flash[:success] = t('views.flash.deleted_archived_conversation_message')
       redirect_to(admin_conversation_message_path(cm))
     else
diff --git a/app/models/channel.rb b/app/models/channel.rb
index baaca3f2..ce6e11cb 100644
--- a/app/models/channel.rb
+++ b/app/models/channel.rb
@@ -118,10 +118,9 @@ def lowercase_name_with_prefix
   # 現在の（キャッシュされていない）最終発言を求める
   # @return [ConversationMessage]
   def current_last_speech
-    conversation_messages.
-      order(timestamp: :desc).
-      limit(1).
-      first
+    conversation_messages
+      .order(timestamp: :desc)
+      .first
   end
 
   # canonical 属性の URL テンプレートを、日付を入れた URL にして返す
diff --git a/app/models/channel_last_speech.rb b/app/models/channel_last_speech.rb
index 3f2a75b2..353fd79a 100644
--- a/app/models/channel_last_speech.rb
+++ b/app/models/channel_last_speech.rb
@@ -11,17 +11,19 @@ class ChannelLastSpeech < ApplicationRecord
 
   # チャンネルの最終発言を更新する
   # @param [Channel] channel 更新対象のチャンネル
-  # @return [self]
+  # @return [ChannelLastSpeech, nil] 更新後の最終発言データ
   def self.refresh!(channel)
-    last_speech = channel.channel_last_speech || new(channel: channel)
+    current_last_speech = channel.current_last_speech
+    unless current_last_speech
+      where(channel: channel)
+        .delete_all
 
-    self.transaction do
-      last_speech.conversation_message = nil
-
-      yield if block_given?
+      return nil
+    end
 
-      last_speech.conversation_message = channel.current_last_speech
-      last_speech.save!
+    find_or_initialize_by(channel: channel).tap do |s|
+      s.conversation_message = current_last_speech
+      s.save!
     end
   end
 end
diff --git a/app/models/conversation_message_archiver.rb b/app/models/conversation_message_archiver.rb
index e3429d9f..ed5bac17 100644
--- a/app/models/conversation_message_archiver.rb
+++ b/app/models/conversation_message_archiver.rb
@@ -12,36 +12,37 @@ class ConversationMessageArchiver
   # @option [String] :archive_reason 非表示理由
   # @return [ArchivedConversationMessage]
   def archive!(params)
-    old_id = params[:old_id].to_i
-    unless cm = ConversationMessage.find(old_id)
+    cm = ConversationMessage.find(params[:old_id].to_i)
+    unless cm
       raise(ArgumentError, 'old_id is required.')
     end
-    archive_reason = params[:archive_reason_id].to_i
-    unless reason = ArchiveReason.find(archive_reason)
-      raise(ArgumentError, 'archive_reason is required.')
+
+    archive_reason = ArchiveReason.find(params[:archive_reason_id].to_i)
+    unless archive_reason
+      raise(ArgumentError, 'archive_reason_id is required.')
     end
 
     am = ArchivedConversationMessage.from_conversation_message(cm)
-    am.archive_reason = reason
+    am.archive_reason = archive_reason
 
     # Mroonga ストレージモードはトランザクション非対応
     ApplicationRecord.transaction do
-      ChannelLastSpeech.refresh!(cm.channel) do
-        am.save!
-        cm.destroy!
-      end
+      am.save!
+      cm.destroy!
+
+      ChannelLastSpeech.refresh!(cm.channel)
     end
 
     am
   end
 
   # Archived -> ConversationMessage
-  # @param [Integer/String] old_id ArchivedConversationMessage.id
-  # @option [String] :id 元の ArchivedConversationMessage.old_id
+  # @param [Integer] archived_conversation_message_id
   # @return [ConversationMessage]
-  def reconstitute!(old_id)
-    unless am = ArchivedConversationMessage.find(old_id.to_i)
-      raise(ArgumentError, 'old_id is required.')
+  def reconstitute!(archived_conversation_message_id)
+    am = ArchivedConversationMessage.find(archived_conversation_message_id)
+    unless am
+      raise(ArgumentError, 'archived_conversation_message_id is required.')
     end
 
     cm = ConversationMessage.new
diff --git a/lib/ircs/plugins/base.rb b/lib/ircs/plugins/base.rb
index 39a5389c..93dcdd62 100644
--- a/lib/ircs/plugins/base.rb
+++ b/lib/ircs/plugins/base.rb
@@ -105,15 +105,6 @@ def record_message_to_channels(message, cinch_channels)
           end
         end
       end
-
-      # [DEPRECATED] チャンネルごとの最終発言を更新する
-      # @param [::Channel] チャンネル
-      # @param [::ConversationMessage] 発言のメッセージ
-      # @return [::ChannelLastSpeech]
-      def update_last_speech!(channel, message)
-        ChannelLastSpeech.refresh!(channel)
-        @logger.warn('このメソッドは廃止予定です。ChannelLastSpeech.refresh! を使ってください')
-      end
     end
   end
 end
diff --git a/test/controllers/channels/today_controller_test.rb b/test/controllers/channels/today_controller_test.rb
index 558734de..8b9245d3 100644
--- a/test/controllers/channels/today_controller_test.rb
+++ b/test/controllers/channels/today_controller_test.rb
@@ -2,14 +2,9 @@
 
 class Channels::TodayControllerTest < ActionController::TestCase
   setup do
-    Channel.delete_all
     @channel = create(:channel)
   end
 
-  teardown do
-    Channel.delete_all
-  end
-
   test '今日のページにリダイレクトされる' do
     today = Time.zone.local(2017, 5, 1)
 
diff --git a/test/controllers/channels/yesterday_controller_test.rb b/test/controllers/channels/yesterday_controller_test.rb
index de1975f5..ceaf2883 100644
--- a/test/controllers/channels/yesterday_controller_test.rb
+++ b/test/controllers/channels/yesterday_controller_test.rb
@@ -2,14 +2,9 @@
 
 class Channels::YesterdayControllerTest < ActionController::TestCase
   setup do
-    Channel.delete_all
     @channel = create(:channel)
   end
 
-  teardown do
-    Channel.delete_all
-  end
-
   test '昨日のページにリダイレクトされる' do
     today = Time.zone.local(2017, 5, 1)
 
diff --git a/test/factories/archive_reasons.rb b/test/factories/archive_reasons.rb
new file mode 100644
index 00000000..328c4a76
--- /dev/null
+++ b/test/factories/archive_reasons.rb
@@ -0,0 +1,11 @@
+FactoryBot.define do
+  factory :archive_reason do
+    reason { '利用規約に違反しているため' }
+
+    initialize_with {
+      ArchiveReason.find_or_initialize_by(reason: reason) do |new_reason|
+        new_reason.attributes = attributes
+      end
+    }
+  end
+end
diff --git a/test/integration/channels_create_test.rb b/test/integration/channels_create_test.rb
index 4f284b11..cc9a0371 100644
--- a/test/integration/channels_create_test.rb
+++ b/test/integration/channels_create_test.rb
@@ -8,15 +8,9 @@ class ChannelsCreateTest < ActionDispatch::IntegrationTest
     @setting = create(:setting)
     @user = create(:user)
 
-    Channel.delete_all
-
     @login_helper = UserLoginTestHelper.new(self, @user, channels_path)
   end
 
-  teardown do
-    Channel.delete_all
-  end
-
   test 'ログインしていない場合、ログインページにリダイレクトされる' do
     @login_helper.assert_redirected_to_login_on_logged_out do
       post(
diff --git a/test/integration/channels_days_show_linking_to_keyword_test.rb b/test/integration/channels_days_show_linking_to_keyword_test.rb
index a88f31b4..aab574c9 100644
--- a/test/integration/channels_days_show_linking_to_keyword_test.rb
+++ b/test/integration/channels_days_show_linking_to_keyword_test.rb
@@ -7,12 +7,6 @@ class ChannelsDaysShowLinkingToKeywordTest < ActionDispatch::IntegrationTest
     create(:setting)
     create(:user)
     @channel = create(:channel)
-
-    PrivmsgKeywordRelationship.delete_all
-    Message.delete_all
-    ConversationMessage.delete_all
-    Keyword.delete_all
-
     @keyword = create(:keyword)
 
     # メッセージの準備
@@ -26,13 +20,6 @@ class ChannelsDaysShowLinkingToKeywordTest < ActionDispatch::IntegrationTest
     @privmsgs = privmsg_factory_ids.map { |id| create(id) }
   end
 
-  teardown do
-    PrivmsgKeywordRelationship.delete_all
-    Message.delete_all
-    ConversationMessage.delete_all
-    Keyword.delete_all
-  end
-
   test 'キーワードのリンク先および表記が正しい' do
     # メッセージとキーワードを関連付ける
     extract_keyword = LogArchiver::ExtractKeyword.new
diff --git a/test/integration/channels_days_show_test.rb b/test/integration/channels_days_show_test.rb
index 78237c32..83299aa8 100644
--- a/test/integration/channels_days_show_test.rb
+++ b/test/integration/channels_days_show_test.rb
@@ -4,11 +4,6 @@ class ChannelsDaysShowTest < ActionDispatch::IntegrationTest
   setup do
     create(:setting)
     create(:user)
-
-    MessageDate.delete_all
-    Message.delete_all
-    ConversationMessage.delete_all
-
     @channel = create(:channel)
 
     # NICK 1件
@@ -45,12 +40,6 @@ class ChannelsDaysShowTest < ActionDispatch::IntegrationTest
                                      style: :normal)
   end
 
-  teardown do
-    MessageDate.delete_all
-    Message.delete_all
-    ConversationMessage.delete_all
-  end
-
   test 'メッセージの一覧が正しく表示される' do
     get(@browse.path)
     assert_response(:success)
diff --git a/test/integration/channels_edit_test.rb b/test/integration/channels_edit_test.rb
index 7b282f7c..aba0b997 100644
--- a/test/integration/channels_edit_test.rb
+++ b/test/integration/channels_edit_test.rb
@@ -9,17 +9,12 @@ class ChannelsEditTest < ActionDispatch::IntegrationTest
     @setting = create(:setting)
     @user = create(:user)
 
-    Channel.delete_all
     @channel = create(:channel)
     @path = edit_channel_path(@channel)
 
     @login_helper = UserLoginTestHelper.new(self, @user, @path)
   end
 
-  teardown do
-    Channel.delete_all
-  end
-
   test 'ログインしている場合、表示される' do
     @login_helper.assert_successful_login_and_get
   end
diff --git a/test/integration/channels_index_test.rb b/test/integration/channels_index_test.rb
index 4c7a7c15..4e24e2ac 100644
--- a/test/integration/channels_index_test.rb
+++ b/test/integration/channels_index_test.rb
@@ -4,15 +4,9 @@ class ChannelsIndexTest < ActionDispatch::IntegrationTest
   setup do
     @setting = create(:setting)
     @user = create(:user)
-
-    Channel.delete_all
     @channel = create(:channel)
   end
 
-  teardown do
-    Channel.delete_all
-  end
-
   test '表示される' do
     get(channels_path)
     assert_response(:success)
diff --git a/test/integration/channels_show_test.rb b/test/integration/channels_show_test.rb
index 56d8a8cc..45185208 100644
--- a/test/integration/channels_show_test.rb
+++ b/test/integration/channels_show_test.rb
@@ -4,15 +4,9 @@ class ChannelsShowTest < ActionDispatch::IntegrationTest
   setup do
     @setting = create(:setting)
     @user = create(:user)
-
-    Channel.delete_all
     @channel = create(:channel)
   end
 
-  teardown do
-    Channel.delete_all
-  end
-
   test '表示される' do
     get(channel_path(@channel))
     assert_response(:success)
diff --git a/test/integration/channels_update_test.rb b/test/integration/channels_update_test.rb
index 00ff9647..45e8b795 100644
--- a/test/integration/channels_update_test.rb
+++ b/test/integration/channels_update_test.rb
@@ -7,18 +7,12 @@ class ChannelsUpdateTest < ActionDispatch::IntegrationTest
   setup do
     @setting = create(:setting)
     @user = create(:user)
-
-    Channel.delete_all
     @channel = create(:channel)
     @path = channel_path(@channel)
 
     @login_helper = UserLoginTestHelper.new(self, @user, @path)
   end
 
-  teardown do
-    Channel.delete_all
-  end
-
   test 'ログインしていない場合、ログインページにリダイレクトされる' do
     @login_helper.assert_redirected_to_login_on_logged_out do
       patch(
diff --git a/test/integration/keywords_show_test.rb b/test/integration/keywords_show_test.rb
index 3bac2d51..2de62c3a 100644
--- a/test/integration/keywords_show_test.rb
+++ b/test/integration/keywords_show_test.rb
@@ -4,12 +4,6 @@ class KeywordsShowTest < ActionDispatch::IntegrationTest
   setup do
     create(:setting)
     create(:user)
-
-    PrivmsgKeywordRelationship.delete_all
-    Message.delete_all
-    ConversationMessage.delete_all
-    Keyword.delete_all
-
     @keyword = create(:keyword)
 
     # メッセージの準備
@@ -23,13 +17,6 @@ class KeywordsShowTest < ActionDispatch::IntegrationTest
     @privmsgs = privmsg_factory_ids.map { |id| create(id) }
   end
 
-  teardown do
-    PrivmsgKeywordRelationship.delete_all
-    Message.delete_all
-    ConversationMessage.delete_all
-    Keyword.delete_all
-  end
-
   test 'キーワードを含む日が1つにまとめられる' do
     # メッセージとキーワードを関連付ける
     @privmsgs.each do |privmsg|
diff --git a/test/integration/users_create_test.rb b/test/integration/users_create_test.rb
index c046047b..4931059d 100644
--- a/test/integration/users_create_test.rb
+++ b/test/integration/users_create_test.rb
@@ -6,17 +6,11 @@
 class UsersCreateTest < ActionDispatch::IntegrationTest
   setup do
     @setting = create(:setting)
-
-    User.delete_all
     @user = create(:user)
 
     @login_helper = UserLoginTestHelper.new(self, @user, users_path)
   end
 
-  teardown do
-    User.delete_all
-  end
-
   test 'ログインしていない場合、ログインページにリダイレクトされる' do
     @login_helper.assert_redirected_to_login_on_logged_out do
       post(
diff --git a/test/integration/users_edit_test.rb b/test/integration/users_edit_test.rb
index f0d433d4..9902106d 100644
--- a/test/integration/users_edit_test.rb
+++ b/test/integration/users_edit_test.rb
@@ -7,18 +7,12 @@
 class UsersEditTest < ActionDispatch::IntegrationTest
   setup do
     @setting = create(:setting)
-
-    User.delete_all
     @user = create(:user)
     @path = edit_user_path(@user)
 
     @login_helper = UserLoginTestHelper.new(self, @user, @path)
   end
 
-  teardown do
-    User.delete_all
-  end
-
   test 'ログインしている場合、表示される' do
     @login_helper.assert_successful_login_and_get
   end
diff --git a/test/integration/users_index_test.rb b/test/integration/users_index_test.rb
index 893c6645..3ce06ec1 100644
--- a/test/integration/users_index_test.rb
+++ b/test/integration/users_index_test.rb
@@ -7,17 +7,11 @@
 class UsersIndexTest < ActionDispatch::IntegrationTest
   setup do
     @setting = create(:setting)
-
-    User.delete_all
     @user = create(:user)
 
     @login_helper = UserLoginTestHelper.new(self, @user, users_path)
   end
 
-  teardown do
-    User.delete_all
-  end
-
   test 'ログインしている場合、表示される' do
     @login_helper.assert_successful_login_and_get
   end
diff --git a/test/integration/users_new_test.rb b/test/integration/users_new_test.rb
index 27a8e9a7..2dff2fcc 100644
--- a/test/integration/users_new_test.rb
+++ b/test/integration/users_new_test.rb
@@ -7,17 +7,11 @@
 class UsersNewTest < ActionDispatch::IntegrationTest
   setup do
     @setting = create(:setting)
-
-    User.delete_all
     @user = create(:user)
 
     @login_helper = UserLoginTestHelper.new(self, @user, new_user_path)
   end
 
-  teardown do
-    User.delete_all
-  end
-
   test 'ログインしている場合、表示される' do
     @login_helper.assert_successful_login_and_get
   end
diff --git a/test/integration/users_show_test.rb b/test/integration/users_show_test.rb
index 2098e0d7..b322b697 100644
--- a/test/integration/users_show_test.rb
+++ b/test/integration/users_show_test.rb
@@ -7,18 +7,12 @@
 class UsersShowTest < ActionDispatch::IntegrationTest
   setup do
     @setting = create(:setting)
-
-    User.delete_all
     @user = create(:user)
     @path = user_path(@user)
 
     @login_helper = UserLoginTestHelper.new(self, @user, @path)
   end
 
-  teardown do
-    User.delete_all
-  end
-
   test 'ログインしている場合、表示される' do
     @login_helper.assert_successful_login_and_get
   end
diff --git a/test/integration/users_update_test.rb b/test/integration/users_update_test.rb
index 741bf1cd..4d1605c1 100644
--- a/test/integration/users_update_test.rb
+++ b/test/integration/users_update_test.rb
@@ -6,18 +6,12 @@
 class UsersUpdateTest < ActionDispatch::IntegrationTest
   setup do
     @setting = create(:setting)
-
-    User.delete_all
     @user = create(:user)
     @path = user_path(@user)
 
     @login_helper = UserLoginTestHelper.new(self, @user, @path)
   end
 
-  teardown do
-    User.delete_all
-  end
-
   test 'ログインしていない場合、ログインページにリダイレクトされる' do
     @login_helper.assert_redirected_to_login_on_logged_out do
       patch(
diff --git a/test/models/channel_browse/day_test.rb b/test/models/channel_browse/day_test.rb
index c39a0933..5a4a22a8 100644
--- a/test/models/channel_browse/day_test.rb
+++ b/test/models/channel_browse/day_test.rb
@@ -137,8 +137,6 @@ class ChannelBrowse::DayTest < ActiveSupport::TestCase
   end
 
   def prepare_message_dates
-    MessageDate.delete_all
-
     @message_date_20160816 = create(:message_date)
     @message_date_20161231 = create(:message_date_20161231)
     @message_date_20170401 = create(:message_date_20170401)
diff --git a/test/models/channel_browse/month_test.rb b/test/models/channel_browse/month_test.rb
index 996b5226..25a23eef 100644
--- a/test/models/channel_browse/month_test.rb
+++ b/test/models/channel_browse/month_test.rb
@@ -2,6 +2,7 @@
 
 class ChannelBrowse::MonthTest < ActiveSupport::TestCase
   setup do
+    create(:channel)
     @month = build(:channel_browse_month)
   end
 
@@ -82,8 +83,6 @@ class ChannelBrowse::MonthTest < ActiveSupport::TestCase
   end
 
   def prepare_message_dates
-    MessageDate.delete_all
-
     @message_date_20160816 = create(:message_date)
     @message_date_20161231 = create(:message_date_20161231)
     @message_date_20170401 = create(:message_date_20170401)
@@ -97,7 +96,9 @@ def prepare_message_dates
     @month.month = date.month
 
     prev_date = @message_date_20160816.date
+
     prev_month = @month.prev_month
+    refute_nil(prev_month)
 
     assert_equal(@month.channel, prev_month.channel, 'チャンネルが正しい')
     assert_equal(prev_date.year, prev_month.year, '年が正しい')
@@ -123,7 +124,9 @@ def prepare_message_dates
     @month.month = date.month
 
     next_date = @message_date_20170401.date
+
     next_month = @month.next_month
+    refute_nil(next_month)
 
     assert_equal(@month.channel, next_month.channel, 'チャンネルが正しい')
     assert_equal(next_date.year, next_month.year, '年が正しい')
diff --git a/test/models/channel_browse/year_test.rb b/test/models/channel_browse/year_test.rb
index 0000e7c9..465caa83 100644
--- a/test/models/channel_browse/year_test.rb
+++ b/test/models/channel_browse/year_test.rb
@@ -2,6 +2,7 @@
 
 class ChannelBrowse::YearTest < ActiveSupport::TestCase
   setup do
+    create(:channel)
     @year = build(:channel_browse_year)
   end
 
@@ -55,8 +56,6 @@ class ChannelBrowse::YearTest < ActiveSupport::TestCase
   end
 
   def prepare_message_dates
-    MessageDate.delete_all
-
     @message_date_20150123 = create(:message_date_20150123)
     @message_date_20161231 = create(:message_date_20161231)
     @message_date_20170401 = create(:message_date_20170401)
@@ -69,7 +68,9 @@ def prepare_message_dates
     @year.year = date.year
 
     prev_date = @message_date_20150123.date
+
     prev_year = @year.prev_year
+    refute_nil(prev_year)
 
     assert_equal(@year.channel, prev_year.channel, 'チャンネルが正しい')
     assert_equal(prev_date.year, prev_year.year, '年が正しい')
@@ -92,7 +93,9 @@ def prepare_message_dates
     @year.year = date.year
 
     next_date = @message_date_20170401.date
+
     next_year = @year.next_year
+    refute_nil(next_year)
 
     assert_equal(@year.channel, next_year.channel, 'チャンネルが正しい')
     assert_equal(next_date.year, next_year.year, '年が正しい')
diff --git a/test/models/channel_for_channels_index_test.rb b/test/models/channel_for_channels_index_test.rb
new file mode 100644
index 00000000..750ed77f
--- /dev/null
+++ b/test/models/channel_for_channels_index_test.rb
@@ -0,0 +1,18 @@
+require 'test_helper'
+
+class ChannelForChannelsIndexTest < ActiveSupport::TestCase
+  setup do
+    [100, 200, 300, 400, 500].each do |id|
+      create("channel_#{id}".to_sym)
+    end
+
+    [100, 200, 400].each do |id|
+      create("channel_#{id}_last_speech".to_sym)
+    end
+  end
+
+  test 'for_channels_index の順序が正しい' do
+    expected = [100, 400, 200, 300, 500].map { |id| "channel_#{id}" }
+    assert_equal(expected, Channel.for_channels_index.map(&:identifier))
+  end
+end
diff --git a/test/models/channel_last_speech_test.rb b/test/models/channel_last_speech_test.rb
index 2c10c926..35d3047b 100644
--- a/test/models/channel_last_speech_test.rb
+++ b/test/models/channel_last_speech_test.rb
@@ -28,4 +28,26 @@ class ChannelLastSpeechTest < ActiveSupport::TestCase
     @channel_last_speech.conversation_message = nil
     refute(@channel_last_speech.valid?)
   end
+
+  sub_test_case 'refresh!' do
+    test 'チャンネル所属メッセージが複数ある場合、最新のメッセージが選ばれる' do
+      create(:privmsg)
+      privmsg_a = create(:privmsg_keyword_sw_a)
+      create(:privmsg_keyword_sw_k)
+
+      channel_last_speech = ChannelLastSpeech.refresh!(@channel)
+
+      assert_equal(privmsg_a, @channel.last_speech)
+      refute_nil(channel_last_speech)
+    end
+
+    test 'チャンネル所属メッセージが存在しない場合、削除される' do
+      ConversationMessage.destroy_all
+
+      channel_last_speech = ChannelLastSpeech.refresh!(@channel)
+
+      assert_nil(@channel.last_speech)
+      assert_nil(channel_last_speech)
+    end
+  end
 end
diff --git a/test/models/channel_test.rb b/test/models/channel_test.rb
index 8e3d7429..3539d793 100644
--- a/test/models/channel_test.rb
+++ b/test/models/channel_test.rb
@@ -81,21 +81,6 @@ class ChannelTest < ActiveSupport::TestCase
     assert_equal('#camelcasechannel', channel.lowercase_name_with_prefix)
   end
 
-  test 'for_channels_index の順序が正しい' do
-    Channel.delete_all
-
-    [100, 200, 300, 400, 500].each do |id|
-      create("channel_#{id}".to_sym)
-    end
-
-    [100, 200, 400].each do |id|
-      create("channel_#{id}_last_speech".to_sym)
-    end
-
-    expected = [100, 400, 200, 300, 500].map { |id| "channel_#{id}" }
-    assert_equal(expected, Channel.for_channels_index.map(&:identifier))
-  end
-
   test 'from_cinch_message: 該当するチャンネルが返る' do
     cinch_channel = Object.new
     cinch_message = Object.new
diff --git a/test/models/conversation_message_archiver_test.rb b/test/models/conversation_message_archiver_test.rb
new file mode 100644
index 00000000..23ef55f3
--- /dev/null
+++ b/test/models/conversation_message_archiver_test.rb
@@ -0,0 +1,103 @@
+require 'test_helper'
+
+class ConversationMessageArchiverTest < ActiveSupport::TestCase
+  sub_test_case 'archive!' do
+    test '発言をアーカイブする（複数発言存在時）' do
+      privmsg1 = create(:privmsg_rgrb_20140320012345)
+      privmsg2 = create(:privmsg_role_20140320023456)
+      reason = create(:archive_reason)
+
+      channel_last_speech1 = ChannelLastSpeech.refresh!(privmsg1.channel)
+      assert_equal(privmsg2, channel_last_speech1.conversation_message)
+
+      ConversationMessageArchiver.new.archive!({
+        old_id: privmsg2.id,
+        archive_reason_id: reason.id,
+      })
+
+      archived_privmsg2 = ArchivedConversationMessage.find_by(old_id: privmsg2.id)
+      refute_nil(archived_privmsg2)
+
+      keys = [
+        :old_id,
+        :channel_id,
+        :timestamp,
+        :nick,
+        :message,
+        :type,
+        :irc_user_id,
+        :digest,
+      ]
+      expected_attrs = privmsg2.attributes.slice(keys)
+      actual_attrs = archived_privmsg2.attributes.slice(keys)
+      assert_equal(expected_attrs, actual_attrs)
+
+      assert_nil(ConversationMessage.find_by(id: privmsg2.id))
+
+      channel_last_speech2 = ChannelLastSpeech.find_by(channel: privmsg1.channel)
+      assert_equal(privmsg1, channel_last_speech2.conversation_message)
+    end
+
+    test '発言をアーカイブする（発言1つのみ）' do
+      privmsg = create(:privmsg)
+      reason = create(:archive_reason)
+
+      channel_last_speech1 = ChannelLastSpeech.refresh!(privmsg.channel)
+      assert_equal(privmsg, channel_last_speech1.conversation_message)
+
+      ConversationMessageArchiver.new.archive!({
+        old_id: privmsg.id,
+        archive_reason_id: reason.id,
+      })
+
+      archived_privmsg = ArchivedConversationMessage.find_by(old_id: privmsg.id)
+      refute_nil(archived_privmsg)
+
+      keys = [
+        :channel_id,
+        :timestamp,
+        :nick,
+        :message,
+        :type,
+        :irc_user_id,
+        :digest,
+      ]
+      expected_attrs = privmsg.attributes.slice(keys)
+      actual_attrs = archived_privmsg.attributes.slice(keys)
+      assert_equal(expected_attrs, actual_attrs)
+
+      assert_nil(ConversationMessage.find_by(id: privmsg.id))
+
+      channel_last_speech2 = ChannelLastSpeech.find_by(channel: privmsg.channel)
+      assert_nil(channel_last_speech2)
+    end
+  end
+
+  test 'reconstitute! はアーカイブされた発言を元に戻す' do
+    privmsg1 = create(:privmsg_rgrb_20140320012345)
+    privmsg2 = create(:privmsg_role_20140320023456)
+    reason = create(:archive_reason)
+
+    ConversationMessageArchiver.new.archive!({
+      old_id: privmsg2.id,
+      archive_reason_id: reason.id,
+    })
+
+    archived_privmsg2 = ArchivedConversationMessage.find_by(old_id: privmsg2.id)
+    refute_nil(archived_privmsg2)
+
+    channel_last_speech1 = ChannelLastSpeech.find_by(channel: privmsg1.channel)
+    assert_equal(privmsg1, channel_last_speech1.conversation_message)
+
+    ConversationMessageArchiver.new.reconstitute!(archived_privmsg2.id)
+
+    archived_privmsg2_2 = ArchivedConversationMessage.find_by(old_id: privmsg2.id)
+    assert_nil(archived_privmsg2_2)
+
+    restored_privmsg2 = ConversationMessage.find(privmsg2.id)
+    assert_equal(privmsg2, restored_privmsg2)
+
+    channel_last_speech2 = ChannelLastSpeech.find_by(channel: privmsg1.channel)
+    assert_equal(restored_privmsg2, channel_last_speech2.conversation_message)
+  end
+end
diff --git a/test/models/message_date_test.rb b/test/models/message_date_test.rb
index 94062efb..2713838c 100644
--- a/test/models/message_date_test.rb
+++ b/test/models/message_date_test.rb
@@ -20,8 +20,6 @@ class MessageDateTest < ActiveSupport::TestCase
   end
 
   def prepare_message_dates
-    MessageDate.delete_all
-
     @message_date_20150123 = create(:message_date_20150123)
     @message_date_20160816 = create(:message_date)
     @message_date_20161231 = create(:message_date_20161231)
diff --git a/test/models/message_period_test.rb b/test/models/message_period_test.rb
index 8f3d7da0..ad205dde 100644
--- a/test/models/message_period_test.rb
+++ b/test/models/message_period_test.rb
@@ -3,14 +3,6 @@
 class MessagePeriodTest < ActiveSupport::TestCase
   setup do
     @period = build(:message_period)
-
-    Message.delete_all
-    ConversationMessage.delete_all
-  end
-
-  teardown do
-    Message.delete_all
-    ConversationMessage.delete_all
   end
 
   test '有効である' do
diff --git a/test/models/message_search_test.rb b/test/models/message_search_test.rb
index dabe1d7c..2ff521d6 100644
--- a/test/models/message_search_test.rb
+++ b/test/models/message_search_test.rb
@@ -3,12 +3,6 @@
 class MessageSearchTest < ActiveSupport::TestCase
   setup do
     @search = build(:message_search)
-
-    ConversationMessage.delete_all
-  end
-
-  teardown do
-    ConversationMessage.delete_all
   end
 
   test '有効である' do
diff --git a/test/system/channel_days_index_chart_test.rb b/test/system/channel_days_index_chart_test.rb
index b55471ce..4ac40487 100644
--- a/test/system/channel_days_index_chart_test.rb
+++ b/test/system/channel_days_index_chart_test.rb
@@ -13,9 +13,6 @@ class ChannelDaysIndexChartTest < ApplicationSystemTestCase
 
     @channel = create(:channel)
 
-    MessageDate.delete_all
-    ConversationMessage.delete_all
-
     create(:privmsg_rgrb_20140320012345)
     create(:message_date_20140320)
 
@@ -28,11 +25,6 @@ class ChannelDaysIndexChartTest < ApplicationSystemTestCase
     )
   end
 
-  teardown do
-    MessageDate.delete_all
-    ConversationMessage.delete_all
-  end
-
   test '月のページにおいてグラフが描画されている' do
     visit(@browse_month.path)
 
diff --git a/test/system/message_filter_test.rb b/test/system/message_filter_test.rb
index a9bb5a0e..8baee015 100644
--- a/test/system/message_filter_test.rb
+++ b/test/system/message_filter_test.rb
@@ -17,9 +17,6 @@ class MessageFilterTest < ApplicationSystemTestCase
     create(:setting)
     create(:user)
 
-    Message.delete_all
-    ConversationMessage.delete_all
-
     @channel = create(:channel)
 
     create_speeches
@@ -36,11 +33,6 @@ class MessageFilterTest < ApplicationSystemTestCase
     )
   end
 
-  teardown do
-    Message.delete_all
-    ConversationMessage.delete_all
-  end
-
   data(
     '日付ページ' => [->_ { @browse.path }, true],
     '日付ページ生ログ' => [->_ { @browse_raw.path }, false],
diff --git a/test/system/message_list_style_test.rb b/test/system/message_list_style_test.rb
index b364af3c..e2220f67 100644
--- a/test/system/message_list_style_test.rb
+++ b/test/system/message_list_style_test.rb
@@ -13,9 +13,6 @@ class MessageListStyleTest < ApplicationSystemTestCase
 
     @channel = create(:channel)
 
-    MessageDate.delete_all
-    ConversationMessage.delete_all
-
     create(:privmsg_rgrb_20140320012345)
     create(:message_date_20140320)
 
@@ -24,11 +21,6 @@ class MessageListStyleTest < ApplicationSystemTestCase
     @browse_raw = ChannelBrowse::Day.new(channel: @channel, date: date, style: :raw)
   end
 
-  teardown do
-    MessageDate.delete_all
-    ConversationMessage.delete_all
-  end
-
   test '通常表示のとき「生ログ」を押すとCookieが正しく設定される' do
     visit(@browse.path)
 
diff --git a/test/system/messages_period_test.rb b/test/system/messages_period_test.rb
index 46c19a1a..43e414fc 100644
--- a/test/system/messages_period_test.rb
+++ b/test/system/messages_period_test.rb
@@ -7,15 +7,9 @@ class MessagesPeriodTest < ApplicationSystemTestCase
 
   setup do
     create(:setting)
-
-    ConversationMessage.delete_all
     @privmsg = create(:privmsg)
   end
 
-  teardown do
-    ConversationMessage.delete_all
-  end
-
   test '検索結果が正しく表示される' do
     visit(
       messages_period_url(channels: 'irc_test',
diff --git a/test/system/messages_search_test.rb b/test/system/messages_search_test.rb
index 37b3d0ae..e3b7b471 100644
--- a/test/system/messages_search_test.rb
+++ b/test/system/messages_search_test.rb
@@ -7,15 +7,9 @@ class MessagesSearchTest < ApplicationSystemTestCase
 
   setup do
     create(:setting)
-
-    ConversationMessage.delete_all
     @privmsg = create(:privmsg)
   end
 
-  teardown do
-    ConversationMessage.delete_all
-  end
-
   test '検索結果が正しく表示される' do
     visit(messages_search_url(q: 'メッセージ'))
 
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 687b9a67..61e242ce 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -13,15 +13,26 @@
 
 require 'factory_bot_rails'
 
-class ActiveSupport::TestCase
-  # Setup all fixtures in test/fixtures/*.yml for all tests in alphabetical order.
-  fixtures :all
+require 'database_cleaner/active_record'
+
+DatabaseCleaner.strategy = :truncation
 
+class ActiveSupport::TestCase
   # Add more helper methods to be used by all tests here...
   include FactoryBot::Syntax::Methods
 
   include ActiveSupport::Testing::TimeHelpers
 
+  self.use_transactional_tests = false
+
+  setup do
+    DatabaseCleaner.start
+  end
+
+  teardown do
+    DatabaseCleaner.clean
+  end
+
   # ファクトリーからオブジェクトを作成する
   # @param [Array<Symbol>] ids ファクトリーIDの配列
   # @return [Array<Object>] 作成されたオブジェクトの配列