diff --git a/logger.gemspec b/logger.gemspec
index c4bc0ac..8b3f706 100644
--- a/logger.gemspec
+++ b/logger.gemspec
@@ -1,7 +1,7 @@
 begin
   require_relative "lib/logger/version"
 rescue LoadError # Fallback to load version file in ruby core repository
-  require_relative "logger/version"
+  require_relative "version"
 end
 
 Gem::Specification.new do |spec|
diff --git a/test/logger/helper.rb b/test/logger/helper.rb
index f11720b..9eaeb20 100644
--- a/test/logger/helper.rb
+++ b/test/logger/helper.rb
@@ -3,6 +3,11 @@
 $LOAD_PATH.unshift File.join(ROOT_DIR, 'test', 'lib') # to use custom test-unit in this repo
 require 'logger'
 require 'test/unit'
-require 'core_assertions'
 
-Test::Unit::TestCase.include Test::Unit::CoreAssertions
+begin
+  # for standalone test suite on ruby/logger
+  require 'core_assertions'
+
+  Test::Unit::TestCase.include Test::Unit::CoreAssertions
+rescue LoadError
+end
diff --git a/test/logger/test_logdevice.rb b/test/logger/test_logdevice.rb
index 28fd675..5adf06e 100644
--- a/test/logger/test_logdevice.rb
+++ b/test/logger/test_logdevice.rb
@@ -30,7 +30,7 @@ def teardown
   end
 
   def d(log, opt = {})
-    Logger::LogDevice.new(log, opt)
+    Logger::LogDevice.new(log, **opt)
   end
 
   def test_initialize