diff --git a/lib/fluent/test/driver/base.rb b/lib/fluent/test/driver/base.rb
index dfd56ac1a9..b53f863db4 100644
--- a/lib/fluent/test/driver/base.rb
+++ b/lib/fluent/test/driver/base.rb
@@ -173,7 +173,7 @@ def instance_shutdown(log: Logger.new($stdout))
 
           if @socket_manager_server
             @socket_manager_server.close
-            if @socket_manager_server.is_a?(String) && File.exist?(@socket_manager_path)
+            if @socket_manager_path.is_a?(String) && File.exist?(@socket_manager_path)
               FileUtils.rm_f @socket_manager_path
             end
           end
diff --git a/test/command/test_fluentd.rb b/test/command/test_fluentd.rb
index 461e19ef1b..5719055521 100644
--- a/test/command/test_fluentd.rb
+++ b/test/command/test_fluentd.rb
@@ -71,6 +71,15 @@ def create_cmdline(conf_path, *fluentd_options)
     end
   end
 
+  def process_kill(pid)
+    begin
+      Process.kill(:TERM, pid) rescue nil
+      Timeout.timeout(10){ sleep 0.1 while process_exist?(pid) }
+    rescue Timeout::Error
+      Process.kill(:KILL, pid) rescue nil
+    end
+  end
+
   def execute_command(cmdline, chdir=@tmp_dir, env = {})
     null_stream = Fluent::FileWrapper.open(File::NULL, 'w')
     gemfile_path = File.expand_path(File.dirname(__FILE__) + "../../../Gemfile")
@@ -85,12 +94,12 @@ def execute_command(cmdline, chdir=@tmp_dir, env = {})
         yield pid, io
         # p(here: "execute command", pid: pid, worker_pids: @worker_pids)
       ensure
-        Process.kill(:KILL, pid) rescue nil
+        process_kill(pid)
         if @supervisor_pid
-          Process.kill(:KILL, @supervisor_pid) rescue nil
+          process_kill(@supervisor_pid)
         end
         @worker_pids.each do |cpid|
-          Process.kill(:KILL, cpid) rescue nil
+          process_kill(cpid)
         end
         # p(here: "execute command", pid: pid, exist: process_exist?(pid), worker_pids: @worker_pids, exists: @worker_pids.map{|i| process_exist?(i) })
         Timeout.timeout(10){ sleep 0.1 while process_exist?(pid) }
diff --git a/test/plugin/test_in_tcp.rb b/test/plugin/test_in_tcp.rb
index b85a919c94..46061cb32c 100755
--- a/test/plugin/test_in_tcp.rb
+++ b/test/plugin/test_in_tcp.rb
@@ -226,6 +226,8 @@ def create_tcp_socket(host, port, &block)
 
       assert_equal 1, d.instance.log.logs.count { |l| l =~ /anonymous client/ }
       assert_equal 0, d.events.size
+    ensure
+      d.instance_shutdown if d&.instance
     end
   end
 
diff --git a/test/plugin/test_out_http.rb b/test/plugin/test_out_http.rb
index e245f74524..b0e1a469a7 100644
--- a/test/plugin/test_out_http.rb
+++ b/test/plugin/test_out_http.rb
@@ -378,6 +378,7 @@ def test_basic_auth_with_invalid_auth
           password hello?
         </auth>
       ])
+      d.instance.system_config_override(root_dir: TMP_DIR) # Backup files are generated in TMP_DIR.
       d.run(default_tag: 'test.http', shutdown: false) do
         test_events.each { |event|
           d.feed(event)
diff --git a/test/plugin/test_output.rb b/test/plugin/test_output.rb
index c25c7b1afb..a04b19d469 100644
--- a/test/plugin/test_output.rb
+++ b/test/plugin/test_output.rb
@@ -803,7 +803,10 @@ def waiting(seconds)
     end
 
     test 'output plugin will call #try_write for plugin supports delayed commit only to flush buffer chunks' do
+      tmp_dir = File.join(__dir__, '../tmp/test_output')
+
       i = create_output(:delayed)
+      i.system_config_override(root_dir: tmp_dir) # Backup files are generated in `tmp_dir`.
       try_write_called = false
       i.register(:try_write){|chunk| try_write_called = true; commit_write(chunk.unique_id) }
 
@@ -820,6 +823,8 @@ def waiting(seconds)
       assert try_write_called
 
       i.stop; i.before_shutdown; i.shutdown; i.after_shutdown; i.close; i.terminate
+    ensure
+      FileUtils.rm_rf(tmp_dir)
     end
 
     test '#prefer_delayed_commit (returns false) decides delayed commit is disabled if both are implemented' do
@@ -849,7 +854,10 @@ def waiting(seconds)
     end
 
     test '#prefer_delayed_commit (returns true) decides delayed commit is enabled if both are implemented' do
+      tmp_dir = File.join(__dir__, '../tmp/test_output')
+
       i = create_output(:full)
+      i.system_config_override(root_dir: tmp_dir) # Backup files are generated in `tmp_dir`.
       write_called = false
       try_write_called = false
       i.register(:write){ |chunk| write_called = true }
@@ -872,6 +880,8 @@ def waiting(seconds)
       assert try_write_called
 
       i.stop; i.before_shutdown; i.shutdown; i.after_shutdown; i.close; i.terminate
+    ensure
+      FileUtils.rm_rf(tmp_dir)
     end
 
     test 'flush_interval is ignored when flush_mode is not interval' do
diff --git a/test/plugin_helper/test_server.rb b/test/plugin_helper/test_server.rb
index 3dc308474b..a08734ae46 100644
--- a/test/plugin_helper/test_server.rb
+++ b/test/plugin_helper/test_server.rb
@@ -37,7 +37,7 @@ class Dummy < Fluent::Plugin::TestBase
     (@d.terminated? || @d.terminate) rescue nil
 
     @socket_manager_server.close
-    if @socket_manager_server.is_a?(String) && File.exist?(@socket_manager_path)
+    if @socket_manager_path.is_a?(String) && File.exist?(@socket_manager_path)
       FileUtils.rm_f @socket_manager_path
     end
   end