diff --git a/.github/workflows/rubocop.yml b/.github/workflows/rubocop.yml
index 798cfb5a3..53675b92f 100644
--- a/.github/workflows/rubocop.yml
+++ b/.github/workflows/rubocop.yml
@@ -13,10 +13,10 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ['3.0', '3.1', '3.2', '3.3']
+        ruby: ['3.0', '3.1', '3.2', '3.3', '3.4']
         os: [ubuntu-latest]
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
diff --git a/.github/workflows/ruby-win.yml b/.github/workflows/ruby-win.yml
index 01533c5fd..bd139bb30 100644
--- a/.github/workflows/ruby-win.yml
+++ b/.github/workflows/ruby-win.yml
@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ '3.3', '3.2', '3.1', '3.0' ]
+        ruby: [ '3.4', '3.3', '3.2', '3.1', '3.0' ]
 
     steps:
     - uses: actions/checkout@v2
diff --git a/.github/workflows/ruby.yml b/.github/workflows/ruby.yml
index 3671376ca..2cbb6222b 100644
--- a/.github/workflows/ruby.yml
+++ b/.github/workflows/ruby.yml
@@ -13,19 +13,18 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ['3.0', '3.1', '3.2', '3.3']
+        ruby: ['3.0', '3.1', '3.2', '3.3', '3.4']
         os: [ubuntu-latest, macOS-latest]
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
     - name: fix ImageMagick policy.xml on Linux
       if: runner.os == 'Linux'
       run: sudo sed -i 's/none/read|write/g' /etc/ImageMagick-6/policy.xml
     - name: Build and test with Rake
       run: |
-        gem install bundler --no-document
-        bundle install --retry 3
         bundle exec rake test
diff --git a/.rubocop.yml b/.rubocop.yml
index 7a007e950..a47a963f3 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -94,8 +94,9 @@ Style/TernaryParentheses:
   Enabled: false
 
 Style/FrozenStringLiteralComment:
-  EnforcedStyle: never
   Enabled: true
+  Exclude:
+    - 'samples/**/*'
 
 Style/SafeNavigation:
   Enabled: false
diff --git a/Gemfile b/Gemfile
index a4da9ae88..fce680bb3 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 
 # Specify your gem's dependencies in review.gemspec
diff --git a/Rakefile b/Rakefile
index b499b060e..f6800a065 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 begin
   require 'bundler'
   Bundler::GemHelper.install_tasks
diff --git a/bin/review b/bin/review
index c96275b29..36e00e7b0 100755
--- a/bin/review
+++ b/bin/review
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # review: Wrapper command to call subcommand
 #
diff --git a/bin/review-catalog-converter b/bin/review-catalog-converter
index bdf28b0cf..52bdfd42e 100755
--- a/bin/review-catalog-converter
+++ b/bin/review-catalog-converter
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2014-2019 Masanori Kado, Kenshi Muto
 #
diff --git a/bin/review-check b/bin/review-check
index 6baba3344..973bd94aa 100755
--- a/bin/review-check
+++ b/bin/review-check
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2010-2019 Kenshi Muto, Minero Aoki
 #               1999-2007 Minero Aoki
diff --git a/bin/review-checkdep b/bin/review-checkdep
index 34ef17cd2..925f35653 100755
--- a/bin/review-checkdep
+++ b/bin/review-checkdep
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2007-2017 Minero Aoki, Kenshi Muto
 #               1999-2007 Minero Aoki
@@ -11,7 +13,7 @@
 
 $LOAD_PATH.unshift(File.realpath('../lib', __dir__))
 
-PREDEF_FILE = 'PREDEF'.freeze
+PREDEF_FILE = 'PREDEF'
 
 def main
   @provided = parse_predefined
diff --git a/bin/review-compile b/bin/review-compile
index 16f79f35d..404d4c93d 100755
--- a/bin/review-compile
+++ b/bin/review-compile
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2008-2019 Kenshi Muto, Masayoshi Takahashi, KADO Masanori, Minero Aoki
 # Copyright (c) 1999-2007 Minero Aoki
@@ -18,7 +20,7 @@ require 'yaml'
 
 include ReVIEW::Loggable
 
-DEFAULT_CONFIG_FILENAME = 'config.yml'.freeze
+DEFAULT_CONFIG_FILENAME = 'config.yml'
 
 def main
   Signal.trap(:INT) { exit 1 }
diff --git a/bin/review-epub2html b/bin/review-epub2html
index fa64acf97..3b6014fa6 100755
--- a/bin/review-epub2html
+++ b/bin/review-epub2html
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2018 Kenshi Muto
 #
diff --git a/bin/review-epubmaker b/bin/review-epubmaker
index 7db68b9ba..f7356caf7 100755
--- a/bin/review-epubmaker
+++ b/bin/review-epubmaker
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2019 Kenshi Muto and Masayoshi Takahashi
 #
 # This program is free software.
diff --git a/bin/review-idgxmlmaker b/bin/review-idgxmlmaker
index 03b2220e6..4cbb1a04f 100755
--- a/bin/review-idgxmlmaker
+++ b/bin/review-idgxmlmaker
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 # Copyright (c) 2019 Kenshi Muto
 #
 # This program is free software.
diff --git a/bin/review-index b/bin/review-index
index 07c0d46b0..d597ca1e0 100755
--- a/bin/review-index
+++ b/bin/review-index
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2008-2020 Minero Aoki, Kenshi Muto
 #               1999-2007 Minero Aoki
diff --git a/bin/review-init b/bin/review-init
index 28940ca6f..68f73bd65 100755
--- a/bin/review-init
+++ b/bin/review-init
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2013-2017 Masanori Kado, Masayoshi Takahashi, Kenshi Muto
 #
diff --git a/bin/review-pdfmaker b/bin/review-pdfmaker
index 7f313b1de..f0b68feba 100755
--- a/bin/review-pdfmaker
+++ b/bin/review-pdfmaker
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2017 Kenshi Muto and Masayoshi Takahashi
 #
 # This program is free software.
diff --git a/bin/review-preproc b/bin/review-preproc
index 54d0a1c11..a69acd92f 100755
--- a/bin/review-preproc
+++ b/bin/review-preproc
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2010-2019 Minero Aoki, Kenshi Muto
 #               1999-2007 Minero Aoki
diff --git a/bin/review-textmaker b/bin/review-textmaker
index 607ba5581..6a553e868 100755
--- a/bin/review-textmaker
+++ b/bin/review-textmaker
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 # Copyright (c) 2018 Kenshi Muto
 #
 # This program is free software.
diff --git a/bin/review-update b/bin/review-update
index 57ddef1fc..fcb890371 100755
--- a/bin/review-update
+++ b/bin/review-update
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2018 Kenshi Muto
 #
diff --git a/bin/review-validate b/bin/review-validate
index 70d53eb11..639e18043 100755
--- a/bin/review-validate
+++ b/bin/review-validate
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2019 Kenshi Muto
 #
 # This program is free software
diff --git a/bin/review-vol b/bin/review-vol
index fccf93f97..d07c14ffd 100755
--- a/bin/review-vol
+++ b/bin/review-vol
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2014-2020 Minero Aoki, Kenshi Muto
 #               2003-2014 Minero Aoki
diff --git a/bin/review-webmaker b/bin/review-webmaker
index b3e891766..a4008bfb5 100755
--- a/bin/review-webmaker
+++ b/bin/review-webmaker
@@ -1,4 +1,6 @@
 #!/usr/bin/env ruby
+# frozen_string_literal: true
+
 #
 # This program is free software.
 # You can distribute or modify this program under the terms of
diff --git a/lib/review.rb b/lib/review.rb
index 4729bc9b6..dcf368edd 100644
--- a/lib/review.rb
+++ b/lib/review.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 Dir["#{__dir__}/review/*.rb"].sort.each do |path|
   require "review/#{File.basename(path, '.rb')}"
 end
diff --git a/lib/review/book.rb b/lib/review/book.rb
index 3e3df80d8..72f85e437 100644
--- a/lib/review/book.rb
+++ b/lib/review/book.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2009-2017 Minero Aoki, Kenshi Muto
 #               2002-2008 Minero Aoki
 #
diff --git a/lib/review/book/base.rb b/lib/review/book/base.rb
index d094d7517..980720450 100644
--- a/lib/review/book/base.rb
+++ b/lib/review/book/base.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Copyright (c) 2009-2023 Minero Aoki, Kenshi Muto, Masayoshi Takahashi
 #               2002-2008 Minero Aoki
 #
@@ -395,7 +396,7 @@ def read_file(filename)
             @logger.warn "!!! #{filename} is obsoleted. please use catalog.yml."
           end
         end
-        res = ''
+        res = +''
         File.open(filename_join(@basedir, filename), 'rt:BOM|utf-8') do |f|
           f.each_line do |line|
             next if line.start_with?('#')
diff --git a/lib/review/book/bib.rb b/lib/review/book/bib.rb
index fb1f66307..2ef24c3c3 100644
--- a/lib/review/book/bib.rb
+++ b/lib/review/book/bib.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2009-2020 Minero Aoki, Kenshi Muto
 #
diff --git a/lib/review/book/book_unit.rb b/lib/review/book/book_unit.rb
index ab0b70dc2..9b0a50635 100644
--- a/lib/review/book/book_unit.rb
+++ b/lib/review/book/book_unit.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2009-2021 Minero Aoki, Kenshi Muto
 #               2002-2008 Minero Aoki
 #
diff --git a/lib/review/book/cache.rb b/lib/review/book/cache.rb
index 27f5f8d78..30eb20ed5 100644
--- a/lib/review/book/cache.rb
+++ b/lib/review/book/cache.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2014-2024 Minero Aoki, Kenshi Muto, Masayoshi Takahashi
 #
diff --git a/lib/review/book/chapter.rb b/lib/review/book/chapter.rb
index c9fc475fd..f6777cc0f 100644
--- a/lib/review/book/chapter.rb
+++ b/lib/review/book/chapter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2009-2019 Minero Aoki, Kenshi Muto
 #               2002-2008 Minero Aoki
diff --git a/lib/review/book/image_finder.rb b/lib/review/book/image_finder.rb
index cd6d89820..86befc9db 100644
--- a/lib/review/book/image_finder.rb
+++ b/lib/review/book/image_finder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2014-2023 Minero Aoki, Kenshi Muto, Masayoshi Takahashi
 #
diff --git a/lib/review/book/index.rb b/lib/review/book/index.rb
index e6e3c4bab..bf2cae90c 100644
--- a/lib/review/book/index.rb
+++ b/lib/review/book/index.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2008-2021 Minero Aoki, Kenshi Muto
 #               2002-2007 Minero Aoki
 #
diff --git a/lib/review/book/index/item.rb b/lib/review/book/index/item.rb
index 87e182613..595a364af 100644
--- a/lib/review/book/index/item.rb
+++ b/lib/review/book/index/item.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2008-2019 Minero Aoki, Kenshi Muto
 #
 # This program is free software.
diff --git a/lib/review/book/page_metric.rb b/lib/review/book/page_metric.rb
index 203563717..af4826a03 100644
--- a/lib/review/book/page_metric.rb
+++ b/lib/review/book/page_metric.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2009-2020 Minero Aoki, Kenshi Muto
 #               2002-2008 Minero Aoki
 #
diff --git a/lib/review/book/part.rb b/lib/review/book/part.rb
index 5e3e2499c..ec1164b03 100644
--- a/lib/review/book/part.rb
+++ b/lib/review/book/part.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2009-2020 Minero Aoki, Kenshi Muto, Masayoshi Takahashi
 #               2002-2008 Minero Aoki
 #
diff --git a/lib/review/book/volume.rb b/lib/review/book/volume.rb
index 980cb2931..adc91dd21 100644
--- a/lib/review/book/volume.rb
+++ b/lib/review/book/volume.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2007-2020 Minero Aoki, Kenshi Muto
 #               2002-2007 Minero Aoki
 #
diff --git a/lib/review/builder.rb b/lib/review/builder.rb
index f78a0b63e..385fd3f2e 100644
--- a/lib/review/builder.rb
+++ b/lib/review/builder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2002-2024 Minero Aoki, Kenshi Muto
 #
 # This program is free software.
diff --git a/lib/review/call_hook.rb b/lib/review/call_hook.rb
index 83a48ff51..2a81a34fb 100644
--- a/lib/review/call_hook.rb
+++ b/lib/review/call_hook.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ReVIEW
   module CallHook
     def call_hook(hook_name, *params, base_dir: nil)
diff --git a/lib/review/catalog.rb b/lib/review/catalog.rb
index 87cbd51c0..53f0ba49f 100644
--- a/lib/review/catalog.rb
+++ b/lib/review/catalog.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'yaml'
 require 'date'
 
diff --git a/lib/review/compiler.rb b/lib/review/compiler.rb
index ea1c5764c..543a2f5fa 100644
--- a/lib/review/compiler.rb
+++ b/lib/review/compiler.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2009-2024 Minero Aoki, Kenshi Muto
 # Copyright (c) 2002-2007 Minero Aoki
 #
@@ -672,7 +674,7 @@ def text(str, block_mode = false)
           error "`@<xxx>' seen but is not valid inline op: #{w}", location: location
         end
       end
-      result = ''
+      result = +''
       until words.empty?
         result << if in_non_escaped_command? && block_mode
                     revert_replace_fence(words.shift)
diff --git a/lib/review/configure.rb b/lib/review/configure.rb
index c80952f7c..a327658b7 100644
--- a/lib/review/configure.rb
+++ b/lib/review/configure.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2012-2022 Masanori Kado, Masayoshi Takahashi, Kenshi Muto
 #
diff --git a/lib/review/converter.rb b/lib/review/converter.rb
index 38c0bb0fa..65a7a48e5 100644
--- a/lib/review/converter.rb
+++ b/lib/review/converter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # This program is free software.
 # You can distribute or modify this program under the terms of
 # the GNU LGPL, Lesser General Public License version 2.1.
diff --git a/lib/review/epub2html.rb b/lib/review/epub2html.rb
index 74e0896c9..c5ef5f96d 100644
--- a/lib/review/epub2html.rb
+++ b/lib/review/epub2html.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2018-2019 Kenshi Muto
 #
diff --git a/lib/review/epubbuilder.rb b/lib/review/epubbuilder.rb
index 5021b0727..06bf2780f 100644
--- a/lib/review/epubbuilder.rb
+++ b/lib/review/epubbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # epubbuilder.rb
 #   just for compatibility
 #
diff --git a/lib/review/epubmaker.rb b/lib/review/epubmaker.rb
index 84491957d..dff22c37e 100644
--- a/lib/review/epubmaker.rb
+++ b/lib/review/epubmaker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2024 Kenshi Muto and Masayoshi Takahashi
 #
 # This program is free software.
diff --git a/lib/review/epubmaker/content.rb b/lib/review/epubmaker/content.rb
index af1c1269d..497822c3a 100644
--- a/lib/review/epubmaker/content.rb
+++ b/lib/review/epubmaker/content.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # = content.rb -- Content object for EPUBMaker.
 #
 # Copyright (c) 2010-2020 Kenshi Muto
diff --git a/lib/review/epubmaker/epubcommon.rb b/lib/review/epubmaker/epubcommon.rb
index b2e6cdf6d..491091f4c 100644
--- a/lib/review/epubmaker/epubcommon.rb
+++ b/lib/review/epubmaker/epubcommon.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # = epubcommon.rb -- super class for EPUBv2 and EPUBv3
 #
 # Copyright (c) 2010-2024 Kenshi Muto and Masayoshi Takahashi
diff --git a/lib/review/epubmaker/epubv2.rb b/lib/review/epubmaker/epubv2.rb
index d262a19bf..ad520f87d 100644
--- a/lib/review/epubmaker/epubv2.rb
+++ b/lib/review/epubmaker/epubv2.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # = epubv2.rb -- EPUB version 2 producer.
 #
 # Copyright (c) 2010-2022 Kenshi Muto and Masayoshi Takahashi
diff --git a/lib/review/epubmaker/epubv3.rb b/lib/review/epubmaker/epubv3.rb
index fec29d6a2..80b3002d8 100644
--- a/lib/review/epubmaker/epubv3.rb
+++ b/lib/review/epubmaker/epubv3.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # = epubv3.rb -- EPUB version 3 producer.
 #
 # Copyright (c) 2010-2023 Kenshi Muto
@@ -41,7 +43,7 @@ def opf
 
         if @opf_prefix && @opf_prefix.size > 0
           prefixes_str = @opf_prefix.map { |k, v| %Q(#{k}: #{v}) }.join(' ')
-          @package_attrs << %Q( prefix="#{prefixes_str}")
+          @package_attrs = %Q( prefix="#{prefixes_str}")
         end
 
         ReVIEW::Template.generate(path: './opf/epubv3.opf.erb', binding: binding)
diff --git a/lib/review/epubmaker/producer.rb b/lib/review/epubmaker/producer.rb
index 7baf1ed04..2577b47ef 100644
--- a/lib/review/epubmaker/producer.rb
+++ b/lib/review/epubmaker/producer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # = producer.rb -- EPUB producer.
 #
 # Copyright (c) 2010-2023 Kenshi Muto
diff --git a/lib/review/epubmaker/reviewheaderlistener.rb b/lib/review/epubmaker/reviewheaderlistener.rb
index ec30c5810..f29098b63 100644
--- a/lib/review/epubmaker/reviewheaderlistener.rb
+++ b/lib/review/epubmaker/reviewheaderlistener.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2018 Kenshi Muto and Masayoshi Takahashi
 #
 # This program is free software.
@@ -20,7 +22,7 @@ class ReVIEWHeaderListener
       include REXML::StreamListener
       def initialize(headlines)
         @level = nil
-        @content = ''
+        @content = +''
         @headlines = headlines
       end
 
@@ -48,7 +50,7 @@ def tag_end(name)
                               'title' => @content,
                               'notoc' => @notoc })
           end
-          @content = ''
+          @content = +''
           @level = nil
           @id = nil
           @notoc = nil
diff --git a/lib/review/epubmaker/zip_exporter.rb b/lib/review/epubmaker/zip_exporter.rb
index 88fab0641..d788de7d0 100644
--- a/lib/review/epubmaker/zip_exporter.rb
+++ b/lib/review/epubmaker/zip_exporter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2017 Kenshi Muto and Masayoshi Takahashi
 #
 # This program is free software.
diff --git a/lib/review/exception.rb b/lib/review/exception.rb
index e53f5fd95..999ecda88 100644
--- a/lib/review/exception.rb
+++ b/lib/review/exception.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2007-2017 Minero Aoki, Kenshi Muto
 #               2002-2007 Minero Aoki
diff --git a/lib/review/extentions.rb b/lib/review/extentions.rb
index d553dd6c8..361b126c1 100644
--- a/lib/review/extentions.rb
+++ b/lib/review/extentions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'review/extentions/object'
 require 'review/extentions/string'
 require 'review/extentions/hash'
diff --git a/lib/review/extentions/hash.rb b/lib/review/extentions/hash.rb
index 9c255002a..58bfbabb3 100644
--- a/lib/review/extentions/hash.rb
+++ b/lib/review/extentions/hash.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Hash
   def deep_merge!(other)
     self.merge!(other) do |_key, v_self, v_other|
diff --git a/lib/review/extentions/object.rb b/lib/review/extentions/object.rb
index 3d22805b8..4f2e2fcd3 100644
--- a/lib/review/extentions/object.rb
+++ b/lib/review/extentions/object.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Object
   def blank?
     respond_to?(:empty?) ? empty? : !self
diff --git a/lib/review/extentions/string.rb b/lib/review/extentions/string.rb
index 9e5f5e968..da26c46f5 100644
--- a/lib/review/extentions/string.rb
+++ b/lib/review/extentions/string.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 if defined?(Encoding) && Encoding.respond_to?(:default_external) &&
    Encoding.default_external != Encoding::UTF_8
   Encoding.default_external = 'UTF-8'
diff --git a/lib/review/htmlbuilder.rb b/lib/review/htmlbuilder.rb
index f00d5af03..2153776d4 100644
--- a/lib/review/htmlbuilder.rb
+++ b/lib/review/htmlbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2008-2023 Minero Aoki, Kenshi Muto, Masayoshi Takahashi,
 #                         KADO Masanori
 #               2002-2007 Minero Aoki
diff --git a/lib/review/htmltoc.rb b/lib/review/htmltoc.rb
index d1220d1ef..89b849157 100644
--- a/lib/review/htmltoc.rb
+++ b/lib/review/htmltoc.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ReVIEW
   class HTMLToc
     def initialize(basedir)
diff --git a/lib/review/htmlutils.rb b/lib/review/htmlutils.rb
index e2810aa8e..4a288d225 100644
--- a/lib/review/htmlutils.rb
+++ b/lib/review/htmlutils.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2006-2018 Minero Aoki, Kenshi Muto
 #               2002-2006 Minero Aoki
diff --git a/lib/review/i18n.rb b/lib/review/i18n.rb
index c186eb050..360de4a74 100644
--- a/lib/review/i18n.rb
+++ b/lib/review/i18n.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'yaml'
 
 module ReVIEW
diff --git a/lib/review/idgxmlbuilder.rb b/lib/review/idgxmlbuilder.rb
index aaefb1f35..196e87db2 100644
--- a/lib/review/idgxmlbuilder.rb
+++ b/lib/review/idgxmlbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2008-2024 Minero Aoki, Kenshi Muto
 #               2002-2007 Minero Aoki
 #
diff --git a/lib/review/idgxmlmaker.rb b/lib/review/idgxmlmaker.rb
index 3acb3144f..e1597999f 100644
--- a/lib/review/idgxmlmaker.rb
+++ b/lib/review/idgxmlmaker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2019-2023 Kenshi Muto
 #
 # This program is free software.
@@ -168,7 +170,7 @@ def build_body(basetmpdir, _yamlfile)
 
     def build_part(part, basetmpdir, xmlfile)
       File.open(File.join(basetmpdir, xmlfile), 'w') do |f|
-        title = ReVIEW::I18n.t('part', part.number)
+        title = +ReVIEW::I18n.t('part', part.number)
         if part.name.strip.present?
           title << ReVIEW::I18n.t('chapter_postfix')
           title << part.name.strip
diff --git a/lib/review/img_graph.rb b/lib/review/img_graph.rb
index e1ab140c7..f1e6b109b 100644
--- a/lib/review/img_graph.rb
+++ b/lib/review/img_graph.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2023 Kenshi Muto
 #
diff --git a/lib/review/img_math.rb b/lib/review/img_math.rb
index 6b24b3b3e..ca496a564 100644
--- a/lib/review/img_math.rb
+++ b/lib/review/img_math.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Copyright (c) 2021-2023 Masayoshi Takahashi, Kenshi Muto
 #
 # This program is free software.
@@ -74,12 +75,15 @@ def make_math_images
       fontsize = @config['imgmath_options']['fontsize'].to_f
       lineheight = @config['imgmath_options']['lineheight'].to_f
 
-      texsrc = default_imgmath_preamble
-      if @config['imgmath_options']['preamble_file'] && File.readable?(@config['imgmath_options']['preamble_file'])
-        texsrc = File.read(@config['imgmath_options']['preamble_file'])
-      end
+      texsrc_pre =
+        if @config['imgmath_options']['preamble_file'] && File.readable?(@config['imgmath_options']['preamble_file'])
+          File.read(@config['imgmath_options']['preamble_file'])
+        else
+          default_imgmath_preamble
+        end
 
-      texsrc << <<-EOB
+      texsrc = <<-EOB
+#{texsrc_pre}
 \\begin{document}
 \\fontsize{#{fontsize}}{#{lineheight}}\\selectfont
 \\input{__IMGMATH_BODY__}
diff --git a/lib/review/index_builder.rb b/lib/review/index_builder.rb
index bd3bfc448..e9c2abd12 100644
--- a/lib/review/index_builder.rb
+++ b/lib/review/index_builder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2008-2022 Minero Aoki, Kenshi Muto, Masayoshi Takahashi,
 #                         KADO Masanori
 #
diff --git a/lib/review/init.rb b/lib/review/init.rb
index d7a5d7717..f6f916dba 100644
--- a/lib/review/init.rb
+++ b/lib/review/init.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2018-2022 Masanori Kado, Masayoshi Takahashi, Kenshi Muto
 #
diff --git a/lib/review/latexbox.rb b/lib/review/latexbox.rb
index 435a07a9e..497335188 100644
--- a/lib/review/latexbox.rb
+++ b/lib/review/latexbox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2021 Kenshi Muto
 #
 # This program is free software.
@@ -13,7 +15,7 @@ def initialize
     end
 
     def tcbox(config)
-      ret = ''
+      ret = +''
 
       %w[column note memo tip info warning important caution notice].each do |name|
         if config['pdfmaker'].nil? || config['pdfmaker']['boxsetting'].nil? ||
diff --git a/lib/review/latexbuilder.rb b/lib/review/latexbuilder.rb
index 491d6a9a0..ce55f9258 100644
--- a/lib/review/latexbuilder.rb
+++ b/lib/review/latexbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2002-2007 Minero Aoki
 #               2008-2009 Minero Aoki, Kenshi Muto
 #               2010-2022 Minero Aoki, Kenshi Muto, TAKAHASHI Masayoshi
@@ -491,7 +493,7 @@ def common_code_block(id, lines, command, caption, _lang)
         puts captionstr
       end
 
-      body = ''
+      body = +''
       lines.each_with_index do |line, idx|
         body.concat(yield(line, idx))
       end
@@ -536,10 +538,10 @@ def make_code_block_args(title, caption, lang, first_line_num: 1)
       if title == 'title' && caption_str == ''
         # ignore
       else
-        args = "#{title}={#{caption_str}}," + args
+        args = "#{title}={#{caption_str}},#{args}"
       end
       if first_line_num != 1
-        args << ",firstnumber=#{first_line_num}"
+        args = "#{args},firstnumber=#{first_line_num}"
       end
       args
     end
@@ -579,11 +581,10 @@ def result_metric(array)
     def image_image(id, caption = '', metric = nil)
       @doc_status[:caption] = true
       captionstr = if @book.config.check_version('2', exception: false)
-                     macro('caption', compile_inline(caption)) + "\n"
+                     macro('caption', compile_inline(caption)) + "\n" + macro('label', image_label(id))
                    else
-                     macro('reviewimagecaption', compile_inline(caption)) + "\n"
+                     macro('reviewimagecaption', compile_inline(caption)) + "\n" + macro('label', image_label(id))
                    end
-      captionstr << macro('label', image_label(id))
       @doc_status[:caption] = nil
 
       metrics = parse_metric('latex', metric)
@@ -820,7 +821,7 @@ def table_begin(ncols)
 
     def separate_tsize(size)
       ret = []
-      s = ''
+      s = +''
       brace = nil
       size.chars.each do |ch|
         case ch
@@ -833,7 +834,7 @@ def separate_tsize(size)
           brace = nil
           s << ch
           ret << s
-          s = ''
+          s = +''
         else
           if brace || s.empty?
             s << ch
@@ -1164,7 +1165,7 @@ def printendnotes
       blank
     end
 
-    BOUTEN = '・'.freeze
+    BOUTEN = '・'
 
     def inline_bou(str)
       macro('reviewbou', escape(str))
diff --git a/lib/review/latexindex.rb b/lib/review/latexindex.rb
index 8c2f269b7..477a6cd8f 100644
--- a/lib/review/latexindex.rb
+++ b/lib/review/latexindex.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2017 Minero Aoki, Kenshi Muto
 #               2002-2006 Minero Aoki
 #
diff --git a/lib/review/latexutils.rb b/lib/review/latexutils.rb
index 04bf44cbc..4f276cee0 100644
--- a/lib/review/latexutils.rb
+++ b/lib/review/latexutils.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2002-2006 Minero Aoki
 # Copyright (c) 2006-2018 Minero Aoki, Kenshi Muto and Masayoshi Takahashi
 #
diff --git a/lib/review/lineinput.rb b/lib/review/lineinput.rb
index ff4d8ea15..e429dee6d 100644
--- a/lib/review/lineinput.rb
+++ b/lib/review/lineinput.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2002-2023 Minero Aoki, Masayoshi Takahashi, Kenshi Muto
 #
diff --git a/lib/review/location.rb b/lib/review/location.rb
index b95c14fc9..43f87c98b 100644
--- a/lib/review/location.rb
+++ b/lib/review/location.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2009-2019 Minero Aoki, Kenshi Muto, Masayoshi Takahashi
 # Copyright (c) 2002-2007 Minero Aoki
 #
diff --git a/lib/review/loggable.rb b/lib/review/loggable.rb
index df2abdcba..d6578287c 100644
--- a/lib/review/loggable.rb
+++ b/lib/review/loggable.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ReVIEW
   module Loggable
     attr_reader :logger
diff --git a/lib/review/logger.rb b/lib/review/logger.rb
index 3ef10daf2..783cced91 100644
--- a/lib/review/logger.rb
+++ b/lib/review/logger.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'logger'
 
 module ReVIEW
diff --git a/lib/review/makerhelper.rb b/lib/review/makerhelper.rb
index 436148632..87619f703 100644
--- a/lib/review/makerhelper.rb
+++ b/lib/review/makerhelper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2012-2023 Yuto HAYAMIZU, Kenshi Muto
 #
 # This program is free software.
diff --git a/lib/review/markdownbuilder.rb b/lib/review/markdownbuilder.rb
index 7cc122678..5df9567da 100644
--- a/lib/review/markdownbuilder.rb
+++ b/lib/review/markdownbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2013-2021 KADO Masanori, Masayoshi Takahashi, Kenshi Muto
 #
 # This program is free software.
diff --git a/lib/review/md2inaobuilder.rb b/lib/review/md2inaobuilder.rb
index 8439ea3f1..674f0f5b2 100644
--- a/lib/review/md2inaobuilder.rb
+++ b/lib/review/md2inaobuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # This program is free software.
 # You can distribute or modify this program under the terms of
 # the GNU LGPL, Lesser General Public License version 2.1.
diff --git a/lib/review/pdfmaker.rb b/lib/review/pdfmaker.rb
index 0c480fa51..bcb7f6b78 100644
--- a/lib/review/pdfmaker.rb
+++ b/lib/review/pdfmaker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2024 Kenshi Muto and Masayoshi Takahashi
 #
 # This program is free software.
@@ -156,7 +158,7 @@ def execute(*args)
     end
 
     def make_input_files(book)
-      input_files = Hash.new { |h, key| h[key] = '' }
+      input_files = Hash.new { |h, key| h[key] = +'' }
       book.parts.each do |part|
         if part.name.present?
           @config['use_part'] = true
@@ -484,7 +486,7 @@ def erb_config
     end
 
     def latex_config
-      result = ReVIEW::Template.generate(path: './latex/config.erb', mode: '-', binding: binding)
+      result = +ReVIEW::Template.generate(path: './latex/config.erb', mode: '-', binding: binding)
       local_config_file = File.join(@basedir, 'layouts', 'config-local.tex.erb')
       if File.exist?(local_config_file)
         result << "%% BEGIN: config-local.tex.erb\n"
diff --git a/lib/review/plaintextbuilder.rb b/lib/review/plaintextbuilder.rb
index 78eebdf95..ee6b9560d 100644
--- a/lib/review/plaintextbuilder.rb
+++ b/lib/review/plaintextbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2018-2023 Kenshi Muto
 #
 # This program is free software.
diff --git a/lib/review/preprocessor.rb b/lib/review/preprocessor.rb
index 955a21897..aa71cfd44 100644
--- a/lib/review/preprocessor.rb
+++ b/lib/review/preprocessor.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2019 Minero Aoki, Kenshi Muto
 #               2002-2009 Minero Aoki
 #
diff --git a/lib/review/preprocessor/directive.rb b/lib/review/preprocessor/directive.rb
index f2a04f4c0..ce025fc73 100644
--- a/lib/review/preprocessor/directive.rb
+++ b/lib/review/preprocessor/directive.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2021 Minero Aoki, Kenshi Muto
 #
 # This program is free software.
diff --git a/lib/review/preprocessor/line.rb b/lib/review/preprocessor/line.rb
index 17947b644..7cb8977e0 100644
--- a/lib/review/preprocessor/line.rb
+++ b/lib/review/preprocessor/line.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2021 Minero Aoki, Kenshi Muto
 #
 # This program is free software.
diff --git a/lib/review/preprocessor/repository.rb b/lib/review/preprocessor/repository.rb
index 5afed36a8..221c968b3 100644
--- a/lib/review/preprocessor/repository.rb
+++ b/lib/review/preprocessor/repository.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2010-2021 Minero Aoki, Kenshi Muto
 #
 # This program is free software.
diff --git a/lib/review/rstbuilder.rb b/lib/review/rstbuilder.rb
index 338624059..9a4d933a8 100644
--- a/lib/review/rstbuilder.rb
+++ b/lib/review/rstbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2008-2020 Minero Aoki, Kenshi Muto
 #               2002-2006 Minero Aoki
 #
diff --git a/lib/review/sec_counter.rb b/lib/review/sec_counter.rb
index 084a7b992..3c2931973 100644
--- a/lib/review/sec_counter.rb
+++ b/lib/review/sec_counter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2008-2017 Minero Aoki, Kenshi Muto, Masayoshi Takahashi,
 #                         KADO Masanori
 #
@@ -32,7 +34,7 @@ def inc(level)
     def anchor(level)
       str = @chapter.format_number(false)
       0.upto(level - 2) do |i|
-        str << "-#{@counter[i]}"
+        str = "#{str}-#{@counter[i]}"
       end
       str
     end
@@ -63,14 +65,15 @@ def prefix(level, secnolevel)
           "#{@chapter.format_number}#{I18n.t('chapter_postfix')}"
         end
       elsif secnolevel >= level
-        prefix = if @chapter.is_a?(ReVIEW::Book::Part)
-                   I18n.t('part_short', @chapter.number)
-                 else
-                   @chapter.format_number(false)
-                 end
+        prefix = []
+        prefix << if @chapter.is_a?(ReVIEW::Book::Part)
+                    I18n.t('part_short', @chapter.number)
+                  else
+                    @chapter.format_number(false)
+                  end
         0.upto(level - 2) { |i| prefix << ".#{@counter[i]}" }
         prefix << I18n.t('chapter_postfix')
-        prefix
+        prefix.join
       end
     end
   end
diff --git a/lib/review/template.rb b/lib/review/template.rb
index dc13f61d8..053cc034a 100644
--- a/lib/review/template.rb
+++ b/lib/review/template.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'erb'
 require 'review/extentions'
 module ReVIEW
diff --git a/lib/review/textbuilder.rb b/lib/review/textbuilder.rb
index 16f39f31c..08cf0d783 100644
--- a/lib/review/textbuilder.rb
+++ b/lib/review/textbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # textbuilder.rb
 #
 # Copyright (c) 2010-2017 Kenshi Muto
diff --git a/lib/review/textmaker.rb b/lib/review/textmaker.rb
index 5ecce2de8..7c02a25ce 100644
--- a/lib/review/textmaker.rb
+++ b/lib/review/textmaker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2018-2023 Kenshi Muto
 #
 # This program is free software.
diff --git a/lib/review/textutils.rb b/lib/review/textutils.rb
index 796327f4b..34904dfe9 100644
--- a/lib/review/textutils.rb
+++ b/lib/review/textutils.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2008-2023 Minero Aoki, Kenshi Muto, Masayoshi Takahashi,
 #                         KADO Masanori
 #               2002-2007 Minero Aoki
diff --git a/lib/review/tocprinter.rb b/lib/review/tocprinter.rb
index e7b86a0ac..770a6b774 100644
--- a/lib/review/tocprinter.rb
+++ b/lib/review/tocprinter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2008-2021 Minero Aoki, Kenshi Muto
 #               1999-2007 Minero Aoki
 #
diff --git a/lib/review/topbuilder.rb b/lib/review/topbuilder.rb
index f7085ff4a..c12408c93 100644
--- a/lib/review/topbuilder.rb
+++ b/lib/review/topbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2008-2022 Minero Aoki, Kenshi Muto
 #               2002-2006 Minero Aoki
 #
diff --git a/lib/review/update.rb b/lib/review/update.rb
index b09354b1c..781ea534d 100644
--- a/lib/review/update.rb
+++ b/lib/review/update.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2018-2023 Kenshi Muto
 #
diff --git a/lib/review/version.rb b/lib/review/version.rb
index e44421a63..e0a33d6ef 100644
--- a/lib/review/version.rb
+++ b/lib/review/version.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ReVIEW
-  VERSION = '5.10.0'.freeze
+  VERSION = '5.10.0'
 end
diff --git a/lib/review/volumeprinter.rb b/lib/review/volumeprinter.rb
index 80de3d553..f9f1cda96 100644
--- a/lib/review/volumeprinter.rb
+++ b/lib/review/volumeprinter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #
 # Copyright (c) 2014-2021 Minero Aoki, Kenshi Muto
 #               2003-2014 Minero Aoki
diff --git a/lib/review/webmaker.rb b/lib/review/webmaker.rb
index e795643bb..8241d847a 100644
--- a/lib/review/webmaker.rb
+++ b/lib/review/webmaker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Copyright (c) 2016-2022 Masayoshi Takahashi, Masanori Kado, Kenshi Muto
 #
 # This program is free software.
diff --git a/lib/review/webtocprinter.rb b/lib/review/webtocprinter.rb
index a3ba25651..c9450b4f9 100644
--- a/lib/review/webtocprinter.rb
+++ b/lib/review/webtocprinter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'review/tocprinter'
 require 'review/i18n'
 require 'review/htmlutils'
@@ -18,7 +20,7 @@ def print_book(book)
     end
 
     def print_result(result_array)
-      content = <<EOT
+      content = +<<EOT
 <ul class="book-toc">
 <li><a href="index.html">TOP</a></li>
 EOT
diff --git a/lib/review/yamlloader.rb b/lib/review/yamlloader.rb
index 11cc1799d..4c3318a18 100644
--- a/lib/review/yamlloader.rb
+++ b/lib/review/yamlloader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'yaml'
 require 'date'
 
diff --git a/review.gemspec b/review.gemspec
index 91c9c3a7f..5a26905d2 100644
--- a/review.gemspec
+++ b/review.gemspec
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 $LOAD_PATH.push(File.expand_path('lib', __dir__))
 require 'review/version'
 
@@ -19,6 +21,7 @@ Gem::Specification.new do |gem|
   gem.extra_rdoc_files = []
   gem.require_paths = ['lib']
 
+  gem.add_dependency('base64')
   gem.add_dependency('csv')
   gem.add_dependency('image_size')
   gem.add_dependency('nkf')
diff --git a/test/book_test_helper.rb b/test/book_test_helper.rb
index caefb2703..1c7a34982 100644
--- a/test/book_test_helper.rb
+++ b/test/book_test_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/book'
 
diff --git a/test/run_test.rb b/test/run_test.rb
index 66d63985e..7fae264a9 100644
--- a/test/run_test.rb
+++ b/test/run_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 base_dir = File.expand_path('..', __dir__)
 lib_dir  = File.join(base_dir, 'lib')
 test_dir = File.join(base_dir, 'test')
diff --git a/test/test_book.rb b/test/test_book.rb
index 176e359d5..c9f6f0c48 100644
--- a/test/test_book.rb
+++ b/test/test_book.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'book_test_helper'
 require 'fileutils'
 
diff --git a/test/test_book_chapter.rb b/test/test_book_chapter.rb
index ffc0b4e7a..9fb83e6a6 100644
--- a/test/test_book_chapter.rb
+++ b/test/test_book_chapter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'book_test_helper'
 
 class ChapterTest < Test::Unit::TestCase
diff --git a/test/test_book_part.rb b/test/test_book_part.rb
index 08fc5d084..ee25e73d3 100644
--- a/test/test_book_part.rb
+++ b/test/test_book_part.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'book_test_helper'
 class PartTest < Test::Unit::TestCase
   include BookTestHelper
diff --git a/test/test_builder.rb b/test/test_builder.rb
index b67a0b8ec..bc76a19e1 100644
--- a/test/test_builder.rb
+++ b/test/test_builder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/builder'
 
diff --git a/test/test_catalog.rb b/test/test_catalog.rb
index 32440cf3c..d39a4052e 100644
--- a/test/test_catalog.rb
+++ b/test/test_catalog.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'book_test_helper'
 require 'review/catalog'
diff --git a/test/test_catalog_converter_cmd.rb b/test/test_catalog_converter_cmd.rb
index c5944e1df..187c76ab7 100644
--- a/test/test_catalog_converter_cmd.rb
+++ b/test/test_catalog_converter_cmd.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'tmpdir'
 require 'fileutils'
diff --git a/test/test_compiler.rb b/test/test_compiler.rb
index 80cea4f1b..217853a94 100644
--- a/test/test_compiler.rb
+++ b/test/test_compiler.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/compiler'
 require 'review/book'
diff --git a/test/test_configure.rb b/test/test_configure.rb
index 3f1eda512..d85daabbc 100644
--- a/test/test_configure.rb
+++ b/test/test_configure.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/epubmaker'
 
diff --git a/test/test_converter.rb b/test/test_converter.rb
index 942a84d90..1e3308469 100644
--- a/test/test_converter.rb
+++ b/test/test_converter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'book_test_helper'
 require 'review/converter'
diff --git a/test/test_epub3maker.rb b/test/test_epub3maker.rb
index 6b7283718..59c399c93 100644
--- a/test/test_epub3maker.rb
+++ b/test/test_epub3maker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/configure'
 require 'review/epubmaker'
diff --git a/test/test_epubmaker.rb b/test/test_epubmaker.rb
index ef3ad77a5..d10b5c6f0 100644
--- a/test/test_epubmaker.rb
+++ b/test/test_epubmaker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/epubmaker'
 
@@ -915,7 +917,8 @@ def test_copy_static_file
       assert_nothing_raised { epubmaker.copy_frontmatter(tmpdir) }
 
       epubmaker.config['titlefile'] = 'nothing.html'
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raise(SystemExit) { epubmaker.copy_frontmatter(tmpdir) }
       assert_equal "ERROR --: titlefile: nothing.html is not found.\n", @log_io.string
     end
@@ -930,7 +933,8 @@ def test_copy_static_file
         assert_nothing_raised { epubmaker.copy_frontmatter(tmpdir) }
 
         epubmaker.config[name] = 'nothing.html'
-        @log_io.string = ''
+        @log_io.rewind
+        @log_io.truncate(0)
         assert_raise(SystemExit) { epubmaker.copy_frontmatter(tmpdir) }
         assert_equal "ERROR --: #{name}: nothing.html is not found.\n", @log_io.string
       end
@@ -945,7 +949,8 @@ def test_copy_static_file
         assert_nothing_raised { epubmaker.copy_backmatter(tmpdir) }
 
         epubmaker.config[name] = 'nothing.html'
-        @log_io.string = ''
+        @log_io.rewind
+        @log_io.truncate(0)
         assert_raise(SystemExit) { epubmaker.copy_backmatter(tmpdir) }
         assert_equal "ERROR --: #{name}: nothing.html is not found.\n", @log_io.string
       end
diff --git a/test/test_epubmaker_cmd.rb b/test/test_epubmaker_cmd.rb
index 77c775646..9f2234f49 100644
--- a/test/test_epubmaker_cmd.rb
+++ b/test/test_epubmaker_cmd.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'tmpdir'
 require 'fileutils'
diff --git a/test/test_extentions_hash.rb b/test/test_extentions_hash.rb
index a416e1943..aa461e278 100644
--- a/test/test_extentions_hash.rb
+++ b/test/test_extentions_hash.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/extentions/hash'
 
diff --git a/test/test_helper.rb b/test/test_helper.rb
index da68b8be8..8497996b5 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 $LOAD_PATH.unshift(File.realpath('../lib', __dir__))
 
 require 'test/unit'
diff --git a/test/test_htmlbuilder.rb b/test/test_htmlbuilder.rb
index 307e32c5f..12ba414b0 100644
--- a/test/test_htmlbuilder.rb
+++ b/test/test_htmlbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'book_test_helper'
 require 'review'
diff --git a/test/test_htmltoc.rb b/test/test_htmltoc.rb
index 188769b79..754a8ef5b 100644
--- a/test/test_htmltoc.rb
+++ b/test/test_htmltoc.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/htmltoc'
 
diff --git a/test/test_htmlutils.rb b/test/test_htmlutils.rb
index 4215c1d35..44a9f314b 100644
--- a/test/test_htmlutils.rb
+++ b/test/test_htmlutils.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/htmlutils'
 
diff --git a/test/test_i18n.rb b/test/test_i18n.rb
index 90c35d080..af399d62f 100644
--- a/test/test_i18n.rb
+++ b/test/test_i18n.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review'
 require 'tmpdir'
diff --git a/test/test_idgxmlbuilder.rb b/test/test_idgxmlbuilder.rb
index c2f2c0a92..a8412ce75 100644
--- a/test/test_idgxmlbuilder.rb
+++ b/test/test_idgxmlbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'book_test_helper'
 require 'review/compiler'
@@ -1147,20 +1149,24 @@ def test_inline_unknown
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<img>{n}\n") }
     assert_match(/unknown image: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<fn>{n}\n") }
     assert_match(/unknown footnote: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<hd>{n}\n") }
     assert_match(/unknown headline: n/, @log_io.string)
     %w[list table column].each do |name|
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raises(ReVIEW::ApplicationError) { compile_block("@<#{name}>{n}\n") }
       assert_match(/unknown #{name}: n/, @log_io.string)
     end
     %w[chap chapref title].each do |name|
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raises(ReVIEW::ApplicationError) { compile_block("@<#{name}>{n}\n") }
       assert_match(/key not found: "n"/, @log_io.string)
     end
diff --git a/test/test_idgxmlmaker_cmd.rb b/test/test_idgxmlmaker_cmd.rb
index edaae9cba..a2fcf6b1f 100644
--- a/test/test_idgxmlmaker_cmd.rb
+++ b/test/test_idgxmlmaker_cmd.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'tmpdir'
 require 'fileutils'
@@ -30,7 +32,7 @@ def common_buildidgxml(bookdir, configfile, targetfile, option)
       Dir.chdir(@tmpdir1) do
         _o, e, s = Open3.capture3("#{ruby_cmd} -S #{REVIEW_IDGXMLMAKER} #{option} #{configfile}")
         if defined?(ReVIEW::TTYLogger)
-          assert_match(/SUCCESS/, e)
+          assert_match(/SUCCESS|INFO/, e) # XXX TTY::Logger should be fixed
         else
           assert_equal '', e
         end
diff --git a/test/test_image_finder.rb b/test/test_image_finder.rb
index b34af5640..e91064792 100644
--- a/test/test_image_finder.rb
+++ b/test/test_image_finder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review'
 require 'review/book/image_finder'
diff --git a/test/test_img_graph.rb b/test/test_img_graph.rb
index ec25d3150..89c760493 100644
--- a/test/test_img_graph.rb
+++ b/test/test_img_graph.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/htmlbuilder'
 require 'review/img_graph'
diff --git a/test/test_img_math.rb b/test/test_img_math.rb
index 4b2c19461..9f41e9882 100644
--- a/test/test_img_math.rb
+++ b/test/test_img_math.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/htmlbuilder'
 require 'review/img_math'
diff --git a/test/test_index.rb b/test/test_index.rb
index 86c91f3ca..47a9ef706 100644
--- a/test/test_index.rb
+++ b/test/test_index.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/compiler'
 require 'review/book'
diff --git a/test/test_indexbuilder.rb b/test/test_indexbuilder.rb
index 8b83ee6fd..f8d11be20 100644
--- a/test/test_indexbuilder.rb
+++ b/test/test_indexbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/builder'
 
diff --git a/test/test_latexbuilder.rb b/test/test_latexbuilder.rb
index 1d6893626..2d80d81e1 100644
--- a/test/test_latexbuilder.rb
+++ b/test/test_latexbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/compiler'
 require 'review/book'
@@ -2491,20 +2493,24 @@ def test_inline_unknown
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<img>{n}\n") }
     assert_match(/unknown image: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<fn>{n}\n") }
     assert_match(/unknown footnote: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<hd>{n}\n") }
     assert_match(/unknown headline: n/, @log_io.string)
     %w[list table column].each do |name|
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raises(ReVIEW::ApplicationError) { compile_block("@<#{name}>{n}\n") }
       assert_match(/unknown #{name}: n/, @log_io.string)
     end
     %w[chap chapref title].each do |name|
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raises(ReVIEW::ApplicationError) { compile_block("@<#{name}>{n}\n") }
       assert_match(/key not found: "n"/, @log_io.string)
     end
diff --git a/test/test_latexbuilder_v2.rb b/test/test_latexbuilder_v2.rb
index d63022e8e..409e0c9e2 100644
--- a/test/test_latexbuilder_v2.rb
+++ b/test/test_latexbuilder_v2.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/compiler'
 require 'review/book'
@@ -1553,20 +1555,24 @@ def test_inline_unknown
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<img>{n}\n") }
     assert_match(/unknown image: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<fn>{n}\n") }
     assert_match(/unknown footnote: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<hd>{n}\n") }
     assert_match(/unknown headline: n/, @log_io.string)
     %w[list table column].each do |name|
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raises(ReVIEW::ApplicationError) { compile_block("@<#{name}>{n}\n") }
       assert_match(/unknown #{name}: n/, @log_io.string)
     end
     %w[chap chapref title].each do |name|
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raises(ReVIEW::ApplicationError) { compile_block("@<#{name}>{n}\n") }
       assert_match(/key not found: "n"/, @log_io.string)
     end
diff --git a/test/test_lineinput.rb b/test/test_lineinput.rb
index 32fb86a33..a754e9309 100644
--- a/test/test_lineinput.rb
+++ b/test/test_lineinput.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/lineinput'
 require 'tempfile'
@@ -6,7 +8,7 @@
 class LineInputTest < Test::Unit::TestCase
   def test_initialize
     io = StringIO.new
-    li = LineInput.new(io)
+    li = ReVIEW::LineInput.new(io)
     assert_equal 0, li.lineno
     assert !li.eof?
     assert_equal "#<ReVIEW::LineInput file=#{io.inspect} line=0>", li.inspect
@@ -23,7 +25,7 @@ def test_gets
   end
 
   def do_test_gets(io)
-    li = LineInput.new(io)
+    li = ReVIEW::LineInput.new(io)
 
     assert_equal "abc\n", li.gets
     assert_equal "def\r\n", li.gets
@@ -41,34 +43,34 @@ def do_test_gets(io)
   end
 
   def test_peek
-    li = LineInput.new(StringIO.new)
+    li = ReVIEW::LineInput.new(StringIO.new)
     assert_equal nil, li.peek
 
-    li = LineInput.new(StringIO.new('abc'))
+    li = ReVIEW::LineInput.new(StringIO.new('abc'))
     assert_equal 'abc', li.peek
   end
 
   def test_next?
-    li = LineInput.new(StringIO.new)
+    li = ReVIEW::LineInput.new(StringIO.new)
     assert !li.next?
 
-    li = LineInput.new(StringIO.new('abc'))
+    li = ReVIEW::LineInput.new(StringIO.new('abc'))
     assert li.next?
   end
 
   def test_each
     content = "abc\ndef\nghi"
     io = StringIO.new(content)
-    li = LineInput.new(io)
+    li = ReVIEW::LineInput.new(io)
 
-    data = ''
-    li.each { |l| data << l }
-    assert_equal content, data
+    data = []
+    li.each { |l| data << l } # rubocop:disable Style/MapIntoArray
+    assert_equal content, data.join
   end
 
   def test_while_match
     io = StringIO.new("abc\ndef\nghi")
-    li = LineInput.new(io)
+    li = ReVIEW::LineInput.new(io)
 
     li.while_match(/^[ad]/) do
       # skip
@@ -79,7 +81,7 @@ def test_while_match
 
   def test_until_match
     io = StringIO.new("abc\ndef\nghi")
-    li = LineInput.new(io)
+    li = ReVIEW::LineInput.new(io)
 
     li.until_match(/^[^a]/) do
       # skip
diff --git a/test/test_location.rb b/test/test_location.rb
index 3de4bb06e..10bb3d237 100644
--- a/test/test_location.rb
+++ b/test/test_location.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/compiler'
 
diff --git a/test/test_logger.rb b/test/test_logger.rb
index d041dbe7d..20e3cdb34 100644
--- a/test/test_logger.rb
+++ b/test/test_logger.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/logger'
 
diff --git a/test/test_makerhelper.rb b/test/test_makerhelper.rb
index 1220e49fe..cbaa5553c 100644
--- a/test/test_makerhelper.rb
+++ b/test/test_makerhelper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/makerhelper'
 require 'tmpdir'
diff --git a/test/test_markdownbuilder.rb b/test/test_markdownbuilder.rb
index 224007ba9..4d4be306d 100644
--- a/test/test_markdownbuilder.rb
+++ b/test/test_markdownbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/compiler'
 require 'review/book'
diff --git a/test/test_md2inaobuilder.rb b/test/test_md2inaobuilder.rb
index db9951b4f..d8489878c 100644
--- a/test/test_md2inaobuilder.rb
+++ b/test/test_md2inaobuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/compiler'
 require 'review/book'
diff --git a/test/test_pdfmaker.rb b/test/test_pdfmaker.rb
index 64c80746f..ae8e2d0c2 100644
--- a/test/test_pdfmaker.rb
+++ b/test/test_pdfmaker.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/pdfmaker'
 
@@ -181,7 +183,7 @@ def error!(msg)
         end
         error_msg = @maker.template_content
         assert_match(/template or configuration error:/, error_msg)
-        assert_match(/undefined local variable or method `not_existed_method'/, error_msg)
+        assert_match(/undefined local variable or method ('|`)not_existed_method'/, error_msg)
       end
     end
   end
diff --git a/test/test_pdfmaker_cmd.rb b/test/test_pdfmaker_cmd.rb
index 81ee6cd1d..385512bd2 100644
--- a/test/test_pdfmaker_cmd.rb
+++ b/test/test_pdfmaker_cmd.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'tmpdir'
 require 'fileutils'
diff --git a/test/test_plaintextbuilder.rb b/test/test_plaintextbuilder.rb
index 61a7db450..14d6ca2ac 100644
--- a/test/test_plaintextbuilder.rb
+++ b/test/test_plaintextbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/compiler'
 require 'review/book'
@@ -806,24 +808,29 @@ def test_inline_unknown
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<img>{n}\n") }
     assert_match(/unknown image: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<fn>{n}\n") }
     assert_match(/unknown footnote: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<endnote>{n}\n") }
     assert_match(/unknown endnote: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<hd>{n}\n") }
     assert_match(/unknown headline: n/, @log_io.string)
     %w[list table column].each do |name|
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raises(ReVIEW::ApplicationError) { compile_block("@<#{name}>{n}\n") }
       assert_match(/unknown #{name}: n/, @log_io.string)
     end
     %w[chap chapref title].each do |name|
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raises(ReVIEW::ApplicationError) { compile_block("@<#{name}>{n}\n") }
       assert_match(/key not found: "n"/, @log_io.string)
     end
diff --git a/test/test_preprocessor.rb b/test/test_preprocessor.rb
index 0d59c60b4..df35e7400 100644
--- a/test/test_preprocessor.rb
+++ b/test/test_preprocessor.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/preprocessor'
 require 'stringio'
diff --git a/test/test_review_ext.rb b/test/test_review_ext.rb
index 31d540cd1..76ca59660 100644
--- a/test/test_review_ext.rb
+++ b/test/test_review_ext.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'book_test_helper'
 require 'review/compiler'
diff --git a/test/test_reviewheaderlistener.rb b/test/test_reviewheaderlistener.rb
index b5a892418..4a7e90b3e 100644
--- a/test/test_reviewheaderlistener.rb
+++ b/test/test_reviewheaderlistener.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'rexml/document'
 require 'rexml/streamlistener'
diff --git a/test/test_rstbuilder.rb b/test/test_rstbuilder.rb
index f1850ea58..b8168ce1e 100644
--- a/test/test_rstbuilder.rb
+++ b/test/test_rstbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/compiler'
 require 'review/book'
diff --git a/test/test_sec_counter.rb b/test/test_sec_counter.rb
index 83613f58b..099283af9 100644
--- a/test/test_sec_counter.rb
+++ b/test/test_sec_counter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'book_test_helper'
 require 'review/sec_counter'
diff --git a/test/test_template.rb b/test/test_template.rb
index 8688cad4a..9e11e719d 100644
--- a/test/test_template.rb
+++ b/test/test_template.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/template'
 
diff --git a/test/test_textmaker_cmd.rb b/test/test_textmaker_cmd.rb
index 7046c3a87..f02520fd6 100644
--- a/test/test_textmaker_cmd.rb
+++ b/test/test_textmaker_cmd.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'tmpdir'
 require 'fileutils'
@@ -30,7 +32,7 @@ def common_buildtext(bookdir, configfile, targetfile, option)
       Dir.chdir(@tmpdir1) do
         _o, e, s = Open3.capture3("#{ruby_cmd} -S #{REVIEW_TEXTMAKER} #{option} #{configfile}")
         if defined?(ReVIEW::TTYLogger)
-          assert_match(/SUCCESS/, e)
+          assert_match(/SUCCESS|INFO/, e) # XXX TTY::Logger should be fixed
         else
           assert_equal '', e
         end
diff --git a/test/test_textutils.rb b/test/test_textutils.rb
index 94e10dc92..112e14bce 100644
--- a/test/test_textutils.rb
+++ b/test/test_textutils.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/textutils'
 
diff --git a/test/test_tocprinter.rb b/test/test_tocprinter.rb
index 860918bc9..fb49f9492 100644
--- a/test/test_tocprinter.rb
+++ b/test/test_tocprinter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/tocprinter'
 require 'unicode/eaw'
diff --git a/test/test_topbuilder.rb b/test/test_topbuilder.rb
index 11837a7b7..0ced25d0e 100644
--- a/test/test_topbuilder.rb
+++ b/test/test_topbuilder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/compiler'
 require 'review/book'
@@ -1160,24 +1162,29 @@ def test_inline_unknown
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<img>{n}\n") }
     assert_match(/unknown image: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<fn>{n}\n") }
     assert_match(/unknown footnote: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<endnote>{n}\n") }
     assert_match(/unknown endnote: n/, @log_io.string)
 
-    @log_io.string = ''
+    @log_io.rewind
+    @log_io.truncate(0)
     assert_raises(ReVIEW::ApplicationError) { compile_block("@<hd>{n}\n") }
     assert_match(/unknown headline: n/, @log_io.string)
     %w[list table column].each do |name|
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raises(ReVIEW::ApplicationError) { compile_block("@<#{name}>{n}\n") }
       assert_match(/unknown #{name}: n/, @log_io.string)
     end
     %w[chap chapref title].each do |name|
-      @log_io.string = ''
+      @log_io.rewind
+      @log_io.truncate(0)
       assert_raises(ReVIEW::ApplicationError) { compile_block("@<#{name}>{n}\n") }
       assert_match(/key not found: "n"/, @log_io.string)
     end
diff --git a/test/test_update.rb b/test/test_update.rb
index 3e4619132..2f91b74cd 100644
--- a/test/test_update.rb
+++ b/test/test_update.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/update'
 require 'tmpdir'
diff --git a/test/test_webtocprinter.rb b/test/test_webtocprinter.rb
index a94e998f4..35bc9d03e 100644
--- a/test/test_webtocprinter.rb
+++ b/test/test_webtocprinter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/webtocprinter'
 require 'book_test_helper'
diff --git a/test/test_yamlloader.rb b/test/test_yamlloader.rb
index 988b76901..e75fde21f 100644
--- a/test/test_yamlloader.rb
+++ b/test/test_yamlloader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/yamlloader'
 require 'review/extentions'
diff --git a/test/test_zip_exporter.rb b/test/test_zip_exporter.rb
index e20f9832d..7e7b79a4e 100644
--- a/test/test_zip_exporter.rb
+++ b/test/test_zip_exporter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'review/epubmaker'
 require 'review/epubmaker/zip_exporter'