fix(microservices): fix kafka serilization of class instances

Fix serilization of class instances that doesn't have own toString() implementation and therefore inherit the standard behavior of [object Object]. Add test for inherited classes.

Author: LeonBiersch

packages/microservices/serializers/kafka-request.serializer.ts

@@ -43,7 +43,9 @@ export class KafkaRequestSerializer
       !isNil(value) && !isString(value) && !Buffer.isBuffer(value);
 
     if (isObjectOrArray) {
-      return isPlainObject(value) || Array.isArray(value)
+      return isPlainObject(value) ||
+        Array.isArray(value) ||
+        value.toString == Object.prototype.toString // Prevent default [object Object] behavior
         ? JSON.stringify(value)
         : value.toString();
     } else if (isUndefined(value)) {

packages/microservices/test/serializers/kafka-request.serializer.spec.ts

@@ -75,6 +75,22 @@ describe('KafkaRequestSerializer', () => {
       });
     });
 
+    it('complex object with inherited .toString()', async () => {
+      class ComplexParent {
+        private readonly name = 'complexParent';
+        public toString(): string {
+          return this.name;
+        }
+      }
+
+      class ComplexChild extends ComplexParent {}
+
+      expect(await instance.serialize(new ComplexChild())).to.deep.eq({
+        headers: {},
+        value: 'complexParent',
+      });
+    });
+
     it('complex object without .toString()', async () => {
       class ComplexWithOutToString {
         private readonly name = 'complex';
@@ -83,7 +99,7 @@ describe('KafkaRequestSerializer', () => {
       expect(await instance.serialize(new ComplexWithOutToString())).to.deep.eq(
         {
           headers: {},
-          value: '[object Object]',
+          value: '{"name":"complex"}',
         },
       );
     });