Add test for json_name functionality
diff --git a/ruby/tests/generated_code.proto b/ruby/tests/generated_code.proto
index e811669..bfdfa5a 100644
--- a/ruby/tests/generated_code.proto
+++ b/ruby/tests/generated_code.proto
@@ -83,3 +83,7 @@
   map<string, TestUnknown> map_unknown = 67;
   int32 unknown_field = 89;
 }
+
+message TestJsonName {
+  int32 value = 1 [json_name = "CustomJsonName"];
+}