3 files changed, 3 insertions, 0 deletions
diff --git a/test/thread/test_cv.rb b/test/thread/test_cv.rb
index b399b479f4..53c7d279b4 100644
--- a/test/thread/test_cv.rb
+++ b/test/thread/test_cv.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 require 'test/unit'
 require 'thread'
 require 'tmpdir'
diff --git a/test/thread/test_queue.rb b/test/thread/test_queue.rb
index 0a1ae48387..32662babed 100644
--- a/test/thread/test_queue.rb
+++ b/test/thread/test_queue.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 require 'test/unit'
 require 'thread'
 require 'tmpdir'
diff --git a/test/thread/test_sync.rb b/test/thread/test_sync.rb
index 9509cac6c7..e576fc1d32 100644
--- a/test/thread/test_sync.rb
+++ b/test/thread/test_sync.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 require 'test/unit'
 require 'sync'
 require 'timeout'