Fix checkLuxonDateTime

While adding a test, it seemed that the format tokens were not correct.
Fixed those as well.

Author: abzainuddin

src/Casts.js

@@ -24,13 +24,13 @@ function checkMomentInstance(attr, value) {
 
 function checkLuxonDateTime(attr, value) {
     invariant(
-        moment.isMoment(value),
-        `Attribute \`${attr}\` is not a luxon DateTime.`
+        DateTime.isDateTime(value),
+        `Attribute \`${attr}\` is not a luxon instance.`
     );
 }
 
 const LUXON_DATE_FORMAT = 'yyyy-LL-dd';
-const LUXON_DATETIME_FORMAT = 'yyy-LL-ddTHH:mm:ssZZZ';
+const LUXON_DATETIME_FORMAT = "yyyy'-'LL'-'dd'T'HH':'mm':'ssZZ";
 
 const CASTS = {
     momentDate: {
@@ -70,7 +70,7 @@ const CASTS = {
             if (value === null || value === undefined) {
                 return null;
             }
-            return DateTime.fromFormat(value, LUXON_DATE_FORMAT);
+            return DateTime.fromISO(value);
         },
         toJS(attr, value) {
             if (value === null || value === undefined) {
@@ -86,7 +86,8 @@ const CASTS = {
             if (value === null) {
                 return null;
             }
-            return DateTime.fromFormat(value, LUXON_DATETIME_FORMAT);
+
+            return DateTime.fromISO(value);
         },
         toJS(attr, value) {
             if (value === null) {

src/__tests__/Casts/datetime.js

@@ -1,5 +1,6 @@
 import { Model, Casts } from '../../';
 import { observable } from 'mobx';
+import { Settings } from 'luxon';
 import moment from 'moment';
 import momentLocale from 'moment/min/moment-with-locales';
 
@@ -79,3 +80,39 @@ test('moment instance with locale should be recognized', () => {
     animal.bornAt = momentLocale('2017-03-22T22:08:23+00:00');
     expect(animal.toJS().bornAt).toEqual(expect.stringContaining('2017-03-22'));
 });
+
+describe('luxon compatibility', () => {
+    Settings.defaultZoneName = 'utc';
+
+    class LuxonAnimal extends Animal {
+        @observable createdAt = '';
+
+        casts() {
+            return {
+                bornAt: Casts.luxonDatetime,
+            };
+        }
+    };
+
+    test('toJS() should throw error when luxon instance is gone', () => {
+        const animal = new LuxonAnimal({ bornAt: '2017-03-22T22:08:23+00:00' });
+
+        animal.bornAt = 'asdf';
+
+        expect(() => {
+            return animal.toJS();
+        }).toThrow('Attribute `bornAt` is not a luxon instance.');
+    });
+
+    test('should be serialized in toBackend()', () => {
+        const animal = new LuxonAnimal({ bornAt: '2017-03-22T22:08:23+00:00' });
+
+        expect(animal.toBackend().born_at).toEqual('2017-03-22T22:08:23+00:00');
+    });
+
+    test('should be serialized in toBackend() when given a binder specific format', () => {
+        const animal = new LuxonAnimal({ bornAt: '2017-03-22T22:08:23.575242+0000' });
+
+        expect(animal.toBackend().born_at).toEqual('2017-03-22T22:08:23+00:00');
+    });
+});

src/__tests__/Model.js

@@ -2,7 +2,7 @@ import axios from 'axios';
 import { toJS, observable } from 'mobx';
 import MockAdapter from 'axios-mock-adapter';
 import _ from 'lodash';
-import { Model, BinderApi } from '../';
+import { Model, BinderApi, Casts } from '../';
 import {
     Animal,
     AnimalStore,