Fix convert UTCDate

Author: dab246

lib/http/converter/utc_date_converter.dart

@@ -8,5 +8,5 @@ class UTCDateConverter implements JsonConverter<UTCDate, String> {
   UTCDate fromJson(String json) => UTCDate(DateTime.parse(json).toUtc());
 
   @override
-  String toJson(UTCDate object) => object.value.toUtc().toString();
+  String toJson(UTCDate object) => object.value.toUtc().toIso8601String();
 }

lib/http/converter/utc_date_nullable_converter.dart

@@ -8,5 +8,5 @@ class UTCDateNullableConverter implements JsonConverter<UTCDate?, String?> {
   UTCDate? fromJson(String? json) => json != null ? UTCDate(DateTime.parse(json).toUtc()) : null;
 
   @override
-  String? toJson(UTCDate? object) => object?.value.toUtc().toString();
+  String? toJson(UTCDate? object) => object?.value.toUtc().toIso8601String();
 }

test/jmap/core/utc_date_converter_test.dart

@@ -0,0 +1,33 @@
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:jmap_dart_client/http/converter/utc_date_converter.dart';
+import 'package:jmap_dart_client/http/converter/utc_date_nullable_converter.dart';
+import 'package:jmap_dart_client/jmap/core/utc_date.dart';
+
+void main() {
+
+  final utcDateStringTest = '2021-10-04T04:39:56.000Z';
+  final expectUTCDate = UTCDate(DateTime.parse('2021-10-04T04:39:56.000Z').toUtc());
+  final testUTCDate = UTCDate(DateTime.parse('2021-10-04T04:39:56.000Z').toUtc());
+  final expectUTCDateString = '2021-10-04T04:39:56.000Z';
+
+  group('UTCDateConverter', () {
+    test('should return UTCDate when receive a properly formatted json', () {
+      expect(expectUTCDate, UTCDateConverter().fromJson(utcDateStringTest));
+    });
+
+    test('should return utc date string valid when receive a utc date', () {
+      expect(expectUTCDateString, UTCDateConverter().toJson(testUTCDate));
+    });
+  });
+
+  group('UTCDateNullableConverter', () {
+    test('should return UTCDate when receive a properly formatted json', () {
+      expect(expectUTCDate, UTCDateNullableConverter().fromJson(utcDateStringTest));
+    });
+
+    test('should return utc date string valid when receive a utc date', () {
+      expect(expectUTCDateString, UTCDateNullableConverter().toJson(testUTCDate));
+    });
+  });
+}