diff --git a/lib/fluent/command/plugin_generator.rb b/lib/fluent/command/plugin_generator.rb
index 6e03e7f5fd..e020c8998e 100644
--- a/lib/fluent/command/plugin_generator.rb
+++ b/lib/fluent/command/plugin_generator.rb
@@ -281,7 +281,7 @@ def initialize
       @text = ""
       @preamble_source = ""
       @preamble = nil
-      open(LICENSE_URL) do |io|
+      URI.open(LICENSE_URL) do |io|
         @text = io.read
       end
       @preamble_source = @text[/^(\s*Copyright.+)/m, 1]
diff --git a/lib/fluent/plugin/parser.rb b/lib/fluent/plugin/parser.rb
index acf3cc6d58..9a6d20a849 100644
--- a/lib/fluent/plugin/parser.rb
+++ b/lib/fluent/plugin/parser.rb
@@ -105,6 +105,12 @@ def parser_type
         :text_per_line
       end
 
+      def initialize
+        super
+
+        @timeout_checker = nil
+      end
+
       def configure(conf)
         super
 
diff --git a/lib/fluent/supervisor.rb b/lib/fluent/supervisor.rb
index 40e3b66f67..f26e248854 100644
--- a/lib/fluent/supervisor.rb
+++ b/lib/fluent/supervisor.rb
@@ -794,7 +794,7 @@ def build_system_config(conf)
           opt[param] = @cl_opt[param]
         end
       end
-      system_config.overwrite_variables(opt)
+      system_config.overwrite_variables(**opt)
       system_config
     end
   end
diff --git a/lib/fluent/test/driver/base.rb b/lib/fluent/test/driver/base.rb
index 6f5aa18e31..dfd56ac1a9 100644
--- a/lib/fluent/test/driver/base.rb
+++ b/lib/fluent/test/driver/base.rb
@@ -22,6 +22,7 @@
 require 'serverengine/socket_manager'
 require 'fileutils'
 require 'timeout'
+require 'logger'
 
 module Fluent
   module Test
@@ -135,16 +136,16 @@ def instance_hook_before_stopped
           # same with above
         end
 
-        def instance_shutdown
+        def instance_shutdown(log: Logger.new($stdout))
           instance_hook_before_stopped
 
           show_errors_if_exists = ->(label, block){
             begin
               block.call
             rescue => e
-              puts "unexpected error while #{label}, #{e.class}:#{e.message}"
+              log.error "unexpected error while #{label}, #{e.class}:#{e.message}"
               e.backtrace.each do |bt|
-                puts "\t#{bt}"
+                log.error "\t#{bt}"
               end
             end
           }
diff --git a/test/config/test_system_config.rb b/test/config/test_system_config.rb
index 32dea77540..b347ae5a2b 100644
--- a/test/config/test_system_config.rb
+++ b/test/config/test_system_config.rb
@@ -68,7 +68,7 @@ def parse_text(text)
       EOS
       s = FakeSupervisor.new
       sc = Fluent::SystemConfig.new(conf)
-      sc.overwrite_variables(s.for_system_config)
+      sc.overwrite_variables(**s.for_system_config)
       assert_equal(1, sc.workers)
       assert_nil(sc.root_dir)
       assert_equal(Fluent::Log::LEVEL_INFO, sc.log_level)
@@ -98,7 +98,7 @@ def parse_text(text)
       EOS
       s = FakeSupervisor.new
       sc = Fluent::SystemConfig.new(conf)
-      sc.overwrite_variables(s.for_system_config)
+      sc.overwrite_variables(**s.for_system_config)
       if k == 'log_level'
         assert_equal(Fluent::Log::LEVEL_ERROR, sc.__send__(k))
       else
@@ -117,7 +117,7 @@ def parse_text(text)
       EOS
       s = FakeSupervisor.new
       sc = Fluent::SystemConfig.new(conf)
-      sc.overwrite_variables(s.for_system_config)
+      sc.overwrite_variables(**s.for_system_config)
       assert_equal(:json, sc.log.format)
       assert_equal('%Y', sc.log.time_format)
     end
@@ -136,7 +136,7 @@ def parse_text(text)
       EOS
       s = FakeSupervisor.new(log_level: level)
       sc = Fluent::SystemConfig.new(conf)
-      sc.overwrite_variables(s.for_system_config)
+      sc.overwrite_variables(**s.for_system_config)
       assert_equal(level, sc.log_level)
     end
   end
diff --git a/test/plugin/test_out_http.rb b/test/plugin/test_out_http.rb
index b755dfdfd4..718cd8319e 100644
--- a/test/plugin/test_out_http.rb
+++ b/test/plugin/test_out_http.rb
@@ -117,7 +117,7 @@ def run_http_server
     Fluent::Test.setup
     FileUtils.rm_rf(TMP_DIR)
 
-    @@result = Result.new(nil, nil, {}, nil)    
+    @@result = Result.new(nil, nil, {}, nil)
     @@http_server_thread ||= Thread.new do
       run_http_server
     end
@@ -230,6 +230,9 @@ def test_write_with_headers
   end
 
   def test_write_with_retryable_response
+    old_report_on_exception = Thread.report_on_exception
+    Thread.report_on_exception = false # thread finished as invalid state since RetryableResponse raises.
+
     d = create_driver("endpoint #{base_endpoint}/503")
     assert_raise(Fluent::Plugin::HTTPOutput::RetryableResponse) do
       d.run(default_tag: 'test.http', shutdown: false) do
@@ -238,7 +241,10 @@ def test_write_with_retryable_response
         }
       end
     end
-    d.instance_shutdown
+
+    d.instance_shutdown(log: $log)
+  ensure
+    Thread.report_on_exception = old_report_on_exception
   end
 
   def test_write_with_disabled_unrecoverable
diff --git a/test/test_supervisor.rb b/test/test_supervisor.rb
index 7808cca6b4..48d87fec9d 100644
--- a/test/test_supervisor.rb
+++ b/test/test_supervisor.rb
@@ -409,6 +409,8 @@ def test_logger_with_rotate_age_and_rotate_size(rotate_age)
   end
 
   def test_inline_config
+    omit 'this feature is deprecated. see https://github.com/fluent/fluentd/issues/2711'
+
     opts = Fluent::Supervisor.default_options
     opts[:inline_config] = '-'
     sv = Fluent::Supervisor.new(opts)