Ignored loading CoreAssertions in test runner

Rakefile

@@ -5,6 +5,8 @@ end
 
 require "rake/testtask"
 Rake::TestTask.new(:test) do |t|
+  t.libs << "test/lib"
+  t.ruby_opts << "-rhelper"
   t.test_files = FileList["test/**/test_*.rb"]
 end
 

test/lib/helper.rb

@@ -0,0 +1,5 @@
+require 'test/unit'
+# for standalone test suite on ruby/logger
+require_relative 'core_assertions'
+
+Test::Unit::TestCase.include Test::Unit::CoreAssertions

test/logger/test_logdevice.rb

@@ -1,6 +1,6 @@
 # coding: US-ASCII
 # frozen_string_literal: false
-require_relative 'helper'
+require 'logger'
 require 'tempfile'
 require 'tmpdir'
 

test/logger/test_logger.rb

@@ -1,6 +1,6 @@
 # coding: US-ASCII
 # frozen_string_literal: false
-require_relative 'helper'
+require 'logger'
 require 'tempfile'
 
 class TestLogger < Test::Unit::TestCase

test/logger/test_logperiod.rb

@@ -1,6 +1,6 @@
 # coding: US-ASCII
 # frozen_string_literal: false
-require_relative 'helper'
+require 'logger'
 require 'time'
 
 class TestLogPeriod < Test::Unit::TestCase

test/logger/test_severity.rb

@@ -1,6 +1,6 @@
 # coding: US-ASCII
 # frozen_string_literal: false
-require_relative 'helper'
+require 'logger'
 
 class TestLoggerSeverity < Test::Unit::TestCase
   def test_enum