3 files changed, 3 insertions, 0 deletions
diff --git a/test/net/smtp/test_response.rb b/test/net/smtp/test_response.rb
index cfd90b18ec..79ac1d2d32 100644
--- a/test/net/smtp/test_response.rb
+++ b/test/net/smtp/test_response.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 require 'net/smtp'
 require 'test/unit'
 
diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index d8bb0c192c..0edb3419d5 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 require 'net/smtp'
 require 'stringio'
 require 'test/unit'
diff --git a/test/net/smtp/test_ssl_socket.rb b/test/net/smtp/test_ssl_socket.rb
index ff229b5ad0..20792190c8 100644
--- a/test/net/smtp/test_ssl_socket.rb
+++ b/test/net/smtp/test_ssl_socket.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: false
 require 'net/smtp'
 require 'test/unit'