diff --git a/test/adapter/json/fields_test.rb b/test/adapter/json/fields_test.rb
index 04da0017..5e1f570a 100644
--- a/test/adapter/json/fields_test.rb
+++ b/test/adapter/json/fields_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 
 module ActiveModelSerializers