diff --git a/samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/ClientTest.java b/samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/ClientTest.java
index e4a9e8440107..9e8b98664252 100644
--- a/samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/ClientTest.java
+++ b/samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/ClientTest.java
@@ -66,5 +66,8 @@ public void testPet() {
         model2.setName("Dog");
 
         Assert.assertTrue(model.equals(model2));
+
+        // test toJson, shouldn't throw exception
+        String test = model.toJson();
     }
 }