diff --git a/Rakefile b/Rakefile
index ff5a5ad05d..8b895d2273 100755
--- a/Rakefile
+++ b/Rakefile
@@ -14,8 +14,8 @@ Rake::TestTask.new(:base_test) do |t|
   #  $ bundle exec rake base_test TEST=test/test_*.rb
   t.libs << "test"
   t.test_files = Dir["test/**/test_*.rb"].sort
-  t.verbose = false
-  t.warning = false
+  t.verbose = true
+  t.warning = true
   t.ruby_opts = ["-Eascii-8bit:ascii-8bit"]
 end
 
diff --git a/lib/fluent/plugin/buffer/file_chunk.rb b/lib/fluent/plugin/buffer/file_chunk.rb
index 5cc097a9fd..f86f6a9deb 100644
--- a/lib/fluent/plugin/buffer/file_chunk.rb
+++ b/lib/fluent/plugin/buffer/file_chunk.rb
@@ -44,6 +44,7 @@ def initialize(metadata, path, mode, perm: system_config.file_permission || FILE
           super(metadata)
           @permission = perm
           @bytesize = @size = @adding_bytes = @adding_size = 0
+          @meta = nil
 
           case mode
           when :create then create_new_chunk(path, perm)
diff --git a/lib/fluent/plugin/filter_record_transformer.rb b/lib/fluent/plugin/filter_record_transformer.rb
index c2ca53ca9d..4f07f7a033 100644
--- a/lib/fluent/plugin/filter_record_transformer.rb
+++ b/lib/fluent/plugin/filter_record_transformer.rb
@@ -315,6 +315,7 @@ def expand(str, placeholders, force_stringify = false)
       class CleanroomExpander
         def expand(__str_to_eval__, tag, time, record, tag_parts, tag_prefix, tag_suffix, hostname)
           tags = tag_parts # for old version compatibility
+          _ = tags # to suppress "unused variable" warning for tags
           Thread.current[:record_transformer_record] = record # for old version compatibility
           instance_eval(__str_to_eval__)
         end
diff --git a/lib/fluent/plugin/output.rb b/lib/fluent/plugin/output.rb
index 088b537b3f..ebfee6b4cb 100644
--- a/lib/fluent/plugin/output.rb
+++ b/lib/fluent/plugin/output.rb
@@ -169,6 +169,12 @@ def initialize
           @buffering = true
         end
         @custom_format = implement?(:custom_format)
+
+        @buffer = nil
+        @secondary = nil
+        @simple_chunking = nil
+        @chunk_keys = @chunk_key_time = @chunk_key_tag = nil
+        @flush_mode = nil
       end
 
       def acts_as_secondary(primary)
@@ -623,8 +629,8 @@ def handle_stream_with_standard_format(tag, es, enqueue: false)
           records += 1
         end
         meta_and_data_bulk = {}
-        meta_and_data.each_pair do |meta, es|
-          meta_and_data_bulk[meta] = [es.to_msgpack_stream(time_int: @time_as_integer), es.size]
+        meta_and_data.each_pair do |meta, m_es|
+          meta_and_data_bulk[meta] = [m_es.to_msgpack_stream(time_int: @time_as_integer), m_es.size]
         end
         write_guard do
           @buffer.write(meta_and_data_bulk, bulk: true, enqueue: enqueue)
@@ -694,7 +700,6 @@ def rollback_write(chunk_id)
       end
 
       def try_rollback_write
-        now = Time.now
         @dequeued_chunks_mutex.synchronize do
           while @dequeued_chunks.first && @dequeued_chunks.first.expired?
             info = @dequeued_chunks.shift
diff --git a/lib/fluent/plugin/storage_local.rb b/lib/fluent/plugin/storage_local.rb
index 16102cb6d9..8c21e84822 100644
--- a/lib/fluent/plugin/storage_local.rb
+++ b/lib/fluent/plugin/storage_local.rb
@@ -34,7 +34,7 @@ def configure(conf)
             @on_memory = true
           end
         elsif @path
-          path = @path.dup
+          # ok
         else # @_plugin_id_configured is true
           raise NotImplementedError, "implement this feature later with system_config"
           ## TODO: get process-wide directory for plugin storage, and generate path for this plugin storage instance
diff --git a/lib/fluent/plugin_helper/event_emitter.rb b/lib/fluent/plugin_helper/event_emitter.rb
index 103a8ef47b..e0b72a2ff7 100644
--- a/lib/fluent/plugin_helper/event_emitter.rb
+++ b/lib/fluent/plugin_helper/event_emitter.rb
@@ -14,7 +14,6 @@
 #    limitations under the License.
 #
 
-require 'fluent/engine'
 require 'fluent/time'
 
 module Fluent
@@ -49,6 +48,7 @@ def initialize
       end
 
       def configure(conf)
+        require 'fluent/engine'
         super
 
         if label_name = conf['@label']
diff --git a/lib/fluent/root_agent.rb b/lib/fluent/root_agent.rb
index 00d3a85b7f..916499bca4 100644
--- a/lib/fluent/root_agent.rb
+++ b/lib/fluent/root_agent.rb
@@ -150,7 +150,7 @@ def flush!
               log.warn_backtrace
             end
           end
-          flushing_threads = []
+          flushing_threads << t
         end
       end
       flushing_threads.each{|t| t.join }
diff --git a/lib/fluent/test/input_test.rb b/lib/fluent/test/input_test.rb
index 98420b8a86..a04d64e9cb 100644
--- a/lib/fluent/test/input_test.rb
+++ b/lib/fluent/test/input_test.rb
@@ -99,14 +99,26 @@ def run_should_stop?
         false
       end
 
+      module EmitStreamWrapper
+        def emit_stream_callee=(method)
+          @emit_stream_callee = method
+        end
+        def emit_stream(tag, es)
+          @emit_stream_callee.call(tag, es)
+        end
+      end
+
       def run(num_waits = 10, &block)
         m = method(:emit_stream)
-        Engine.define_singleton_method(:emit_stream) {|tag,es|
-          m.call(tag, es)
-        }
-        instance.router.define_singleton_method(:emit_stream) {|tag,es|
-          m.call(tag, es)
-        }
+        (class << Engine; self; end).module_eval do
+          prepend EmitStreamWrapper
+        end
+        Engine.emit_stream_callee = m
+        (class << instance.router; self; end).module_eval do
+          prepend EmitStreamWrapper
+        end
+        instance.router.emit_stream_callee = m
+
         super(num_waits) {
           block.call if block
 
diff --git a/lib/fluent/test/output_test.rb b/lib/fluent/test/output_test.rb
index 04c12ab935..d590688507 100644
--- a/lib/fluent/test/output_test.rb
+++ b/lib/fluent/test/output_test.rb
@@ -139,7 +139,6 @@ def run(&block)
             assert_equal(@expected_buffer, buffer)
           end
 
-          chunks = []
           lines.keys.each do |meta|
             chunk = @instance.buffer.generate_chunk(meta)
             chunk.append(lines[meta])
diff --git a/test/config/test_configurable.rb b/test/config/test_configurable.rb
index 3f26824bd0..a8dff79b87 100644
--- a/test/config/test_configurable.rb
+++ b/test/config/test_configurable.rb
@@ -665,14 +665,14 @@ class TestConfigurable < ::Test::Unit::TestCase
           checker = lambda { |conf| ConfigurableSpec::Example0.new.configure(conf) }
 
           assert_nothing_raised { checker.call(complete) }
-          assert_raise(Fluent::ConfigError) { checker.call(complete.reject{|k,v| k == "stringvalue" }) }
-          assert_raise(Fluent::ConfigError) { checker.call(complete.reject{|k,v| k == "boolvalue"   }) }
-          assert_raise(Fluent::ConfigError) { checker.call(complete.reject{|k,v| k == "integervalue"}) }
-          assert_raise(Fluent::ConfigError) { checker.call(complete.reject{|k,v| k == "sizevalue"   }) }
-          assert_raise(Fluent::ConfigError) { checker.call(complete.reject{|k,v| k == "timevalue"   }) }
-          assert_raise(Fluent::ConfigError) { checker.call(complete.reject{|k,v| k == "floatvalue"  }) }
-          assert_raise(Fluent::ConfigError) { checker.call(complete.reject{|k,v| k == "hashvalue"   }) }
-          assert_raise(Fluent::ConfigError) { checker.call(complete.reject{|k,v| k == "arrayvalue"  }) }
+          assert_raise(Fluent::ConfigError) { c = complete.dup; c.delete("stringvalue"); checker.call(c) }
+          assert_raise(Fluent::ConfigError) { c = complete.dup; c.delete("boolvalue"); checker.call(c) }
+          assert_raise(Fluent::ConfigError) { c = complete.dup; c.delete("integervalue"); checker.call(c) }
+          assert_raise(Fluent::ConfigError) { c = complete.dup; c.delete("sizevalue"); checker.call(c) }
+          assert_raise(Fluent::ConfigError) { c = complete.dup; c.delete("timevalue"); checker.call(c) }
+          assert_raise(Fluent::ConfigError) { c = complete.dup; c.delete("floatvalue"); checker.call(c) }
+          assert_raise(Fluent::ConfigError) { c = complete.dup; c.delete("hashvalue"); checker.call(c) }
+          assert_raise(Fluent::ConfigError) { c = complete.dup; c.delete("arrayvalue"); checker.call(c) }
         end
 
         test 'generates section with default values for init:true sections' do
diff --git a/test/plugin/test_filter_record_transformer.rb b/test/plugin/test_filter_record_transformer.rb
index 76e82c4e50..b59ceff620 100644
--- a/test/plugin/test_filter_record_transformer.rb
+++ b/test/plugin/test_filter_record_transformer.rb
@@ -117,13 +117,13 @@ def emit(config, msgs = [''])
       config = %[
         enable_ruby yes
         <record>
-          message ${hostname} ${tag_parts.last} ${URI.encode(message)}
+          message ${hostname} ${tag_parts.last} ${"'" + message + "'"}
         </record>
       ]
       msgs = ['1', '2']
       es = emit(config, msgs)
       es.each_with_index do |(_t, r), i|
-        assert_equal("#{@hostname} #{@tag_parts[-1]} #{msgs[i]}", r['message'])
+        assert_equal("#{@hostname} #{@tag_parts[-1]} '#{msgs[i]}'", r['message'])
       end
     end
 
diff --git a/test/plugin/test_in_http.rb b/test/plugin/test_in_http.rb
index 7e7265893f..bf52aa596a 100644
--- a/test/plugin/test_in_http.rb
+++ b/test/plugin/test_in_http.rb
@@ -251,7 +251,7 @@ def test_with_regexp
         body = record.map { |k, v|
           v.to_s
         }.join(':')
-        res = post("/#{tag}?time=#{_time.to_s}", body)
+        res = post("/#{tag}?time=#{_time.to_s}", body, {'Content-Type' => 'application/octet-stream'})
         assert_equal "200", res.code
       }
     end
@@ -273,7 +273,7 @@ def test_with_csv
     d.run do
       d.expected_emits.each { |tag, _time, record|
         body = record.map { |k, v| v }.to_csv
-        res = post("/#{tag}?time=#{_time.to_s}", body)
+        res = post("/#{tag}?time=#{_time.to_s}", body, {'Content-Type' => 'text/comma-separated-values'})
         assert_equal "200", res.code
       }
     end
@@ -308,7 +308,7 @@ def test_cors_allowed
     begin
       d.run do
         Net::HTTP.start("127.0.0.1", PORT) do |http|
-          req = Net::HTTP::Post.new("/foo/bar", {"Origin" => "http://foo.com"})
+          req = Net::HTTP::Post.new("/foo/bar", {"Origin" => "http://foo.com", "Content-Type" => "application/octet-stream"})
           res = http.request(req)
 
           acao = res["Access-Control-Allow-Origin"]
@@ -333,7 +333,7 @@ def test_cors_disallowed
     begin
       d.run do
         Net::HTTP.start("127.0.0.1", PORT) do |http|
-          req = Net::HTTP::Post.new("/foo/bar", {"Origin" => "http://bar.com"})
+          req = Net::HTTP::Post.new("/foo/bar", {"Origin" => "http://bar.com", "Content-Type" => "application/octet-stream"})
           res = http.request(req)
 
           response_code = res.code
@@ -352,6 +352,10 @@ def test_cors_disallowed
   $test_in_http_content_types = []
   $test_in_http_content_types_flag = false
   module ContentTypeHook
+    def initialize(*args)
+      @io_handler = nil
+      super
+    end
     def on_headers_complete(headers)
       super
       if $test_in_http_content_types_flag
@@ -402,8 +406,14 @@ def post(path, params, header = {})
     http = Net::HTTP.new("127.0.0.1", PORT)
     req = Net::HTTP::Post.new(path, header)
     if params.is_a?(String)
+      unless header.has_key?('Content-Type')
+        header['Content-Type'] = 'application/octet-stream'
+      end
       req.body = params
     else
+      unless header.has_key?('Content-Type')
+        header['Content-Type'] = 'application/x-www-form-urlencoded'
+      end
       req.set_form_data(params)
     end
     http.request(req)
diff --git a/test/plugin/test_output_as_buffered.rb b/test/plugin/test_output_as_buffered.rb
index b7bf1977d8..6793dd5528 100644
--- a/test/plugin/test_output_as_buffered.rb
+++ b/test/plugin/test_output_as_buffered.rb
@@ -272,7 +272,6 @@ def waiting(seconds)
       @i.register(:format){|tag,time,record| [tag,time,record].to_json + "\n" }
       @i.register(:write){|chunk| chunk.read.split("\n").reject{|l| l.empty? }.each{|data| ary << data } }
 
-      tag = "test.tag"
       t = event_time()
       r = {}
       (0...10).each do |i|
@@ -382,7 +381,6 @@ def waiting(seconds)
       @i.register(:format){|tag,time,record| [tag,time,record].to_json + "\n" }
       @i.register(:write){|chunk| chunk.read.split("\n").reject{|l| l.empty? }.each{|data| ary << data } }
 
-      tag = "test.tag"
       t = event_time()
       r = {}
       (0...10).each do |i|
diff --git a/test/plugin/test_output_as_buffered_overflow.rb b/test/plugin/test_output_as_buffered_overflow.rb
index a60d8d7143..acfbfbd71b 100644
--- a/test/plugin/test_output_as_buffered_overflow.rb
+++ b/test/plugin/test_output_as_buffered_overflow.rb
@@ -15,6 +15,10 @@ def register(name, &block)
     end
   end
   class DummyAsyncOutput < DummyBareOutput
+    def initialize
+      super
+      @format = @write = nil
+    end
     def format(tag, time, record)
       @format ? @format.call(tag, time, record) : [tag, time, record].to_json
     end
@@ -37,7 +41,8 @@ def waiting(seconds)
         yield
       end
     rescue Timeout::Error
-      STDERR.print *(@i.log.out.logs)
+      logs = @i.log.out.logs
+      STDERR.print(*logs)
       raise
     end
   end
@@ -133,7 +138,7 @@ def waiting(seconds)
 
       assert !@i.buffer.storable?
 
-      thread = Thread.new do
+      Thread.new do
         sleep 3
         failing = false
       end