Latest json_serializable caught unnoticed issue with example (#209)

Updated test to catch it

Author: kevmoo

example/lib/example.dart

@@ -59,8 +59,8 @@ DateTime _dateTimeFromEpochUs(int us) =>
     new DateTime.fromMicrosecondsSinceEpoch(us);
 int _dateTimeToEpochUs(DateTime dateTime) => dateTime.microsecondsSinceEpoch;
 
-@JsonSerializable(createToJson: false)
-class Item {
+@JsonSerializable()
+class Item extends Object with _$ItemSerializerMixin {
   int count;
   int itemNumber;
   bool isRushed;

example/lib/example.g.dart

@@ -93,6 +93,17 @@ Item _$ItemFromJson(Map<String, dynamic> json) => new Item()
   ..itemNumber = json['itemNumber'] as int
   ..isRushed = json['isRushed'] as bool;
 
+abstract class _$ItemSerializerMixin {
+  int get count;
+  int get itemNumber;
+  bool get isRushed;
+  Map<String, dynamic> toJson() => <String, dynamic>{
+        'count': count,
+        'itemNumber': itemNumber,
+        'isRushed': isRushed
+      };
+}
+
 // **************************************************************************
 // Generator: JsonLiteralGenerator
 // **************************************************************************

example/test/example_test.dart

@@ -10,7 +10,9 @@ import 'package:test/test.dart';
 void main() {
   test('JsonSerializable', () {
     final person = new Person('Inigo', 'Montoya', new DateTime(1560, 5, 5))
-      ..orders = [new Order(new DateTime.now())];
+      ..orders = [
+        new Order(new DateTime.now())..item = (new Item()..count = 42)
+      ];
 
     final personJson = _encode(person);
 
@@ -21,6 +23,7 @@ void main() {
     expect(person.lastName, person2.lastName);
     expect(person.dateOfBirth, person2.dateOfBirth);
     expect(person.orders.single.date, person2.orders.single.date);
+    expect(person.orders.single.item.count, 42);
 
     expect(_encode(person2), equals(personJson));
   });