diff --git a/test/bigdecimal/testbase.rb b/test/bigdecimal/helper.rb
similarity index 100%
rename from test/bigdecimal/testbase.rb
rename to test/bigdecimal/helper.rb
diff --git a/test/bigdecimal/test_bigdecimal.rb b/test/bigdecimal/test_bigdecimal.rb
index e9a86cfb..f94cf9b6 100644
--- a/test/bigdecimal/test_bigdecimal.rb
+++ b/test/bigdecimal/test_bigdecimal.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: false
-require_relative "testbase"
+require_relative "helper"
 require 'bigdecimal/math'
 require 'rbconfig/sizeof'
 
diff --git a/test/bigdecimal/test_bigdecimal_util.rb b/test/bigdecimal/test_bigdecimal_util.rb
index b855fd58..3e3d9db1 100644
--- a/test/bigdecimal/test_bigdecimal_util.rb
+++ b/test/bigdecimal/test_bigdecimal_util.rb
@@ -1,9 +1,10 @@
 # frozen_string_literal: false
-require_relative "testbase"
-
+require_relative "helper"
 require 'bigdecimal/util'
 
 class TestBigDecimalUtil < Test::Unit::TestCase
+  include TestBigDecimalBase
+
   def test_BigDecimal_to_d
     x = BigDecimal(1)
     assert_same(x, x.to_d)
diff --git a/test/bigdecimal/test_bigmath.rb b/test/bigdecimal/test_bigmath.rb
index 6f271d09..5bf1fbf3 100644
--- a/test/bigdecimal/test_bigmath.rb
+++ b/test/bigdecimal/test_bigmath.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: false
-require_relative "testbase"
+require_relative "helper"
 require "bigdecimal/math"
 
 class TestBigMath < Test::Unit::TestCase
diff --git a/test/bigdecimal/test_ractor.rb b/test/bigdecimal/test_ractor.rb
index 3ccd7c80..f78663f1 100644
--- a/test/bigdecimal/test_ractor.rb
+++ b/test/bigdecimal/test_ractor.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
-require_relative "testbase"
+require_relative "helper"
 
 class TestBigDecimalRactor < Test::Unit::TestCase
   include TestBigDecimalBase