diff --git a/test/helper.rb b/test/helper.rb
new file mode 100644
index 0000000000..d29332104b
--- /dev/null
+++ b/test/helper.rb
@@ -0,0 +1,5 @@
+ROOT_DIR = File.dirname(__dir__)
+$LOAD_PATH.unshift File.join(ROOT_DIR, 'lib') # to use logger in this repo instead of ruby built-in logger
+$LOAD_PATH.unshift File.join(ROOT_DIR, 'test', 'lib') # to use custom test-unit in this repo
+require 'logger'
+require 'test/unit'
diff --git a/test/logger/test_logdevice.rb b/test/logger/test_logdevice.rb
index 7d5bf9ac81..30047f89b1 100644
--- a/test/logger/test_logdevice.rb
+++ b/test/logger/test_logdevice.rb
@@ -1,7 +1,6 @@
 # coding: US-ASCII
 # frozen_string_literal: false
-require 'test/unit'
-require 'logger'
+require_relative '../helper'
 require 'tempfile'
 require 'tmpdir'
 
diff --git a/test/logger/test_logger.rb b/test/logger/test_logger.rb
index 3f2319b961..5806e0c685 100644
--- a/test/logger/test_logger.rb
+++ b/test/logger/test_logger.rb
@@ -1,7 +1,6 @@
 # coding: US-ASCII
 # frozen_string_literal: false
-require 'test/unit'
-require 'logger'
+require_relative '../helper'
 require 'tempfile'
 
 class TestLogger < Test::Unit::TestCase
diff --git a/test/logger/test_severity.rb b/test/logger/test_severity.rb
index 8889a1dc52..4da23cdd0f 100644
--- a/test/logger/test_severity.rb
+++ b/test/logger/test_severity.rb
@@ -1,7 +1,6 @@
 # coding: US-ASCII
 # frozen_string_literal: false
-require 'test/unit'
-require 'logger'
+require_relative '../helper'
 
 class TestLoggerSeverity < Test::Unit::TestCase
   def test_enum
@@ -13,13 +12,13 @@ class TestLoggerSeverity < Test::Unit::TestCase
     end
     assert_equal(levels.size, Logger::Severity.constants.size)
   end
-  
+
   def test_level_assignment
     logger = Logger.new(nil)
-    
+
     Logger::Severity.constants.each do |level|
       next if level == :UNKNOWN
-      
+
       logger.send("#{level.downcase}!")
       assert(logger.level) == Logger::Severity.const_get(level)
     end