refactor: jsonFixture file

Author: sachaarbonel

packages/stream_feed/test/fixtures/realtime_message.json

@@ -0,0 +1,19 @@
+{
+    "deleted": [],
+    "deleted_foreign_ids": [],
+    "feed": "reward:1",
+    "new": [
+      {
+        "actor": "reward:1",
+        "foreign_id": null,
+        "id": "f3de8328-be2d-11eb-bb18-128a130028af",
+        "message": "@Jessica check out getstream.io it's so dang awesome.",
+        "object": "tweet:id",
+        "origin": null,
+        "target": null,
+        "time": "2021-05-26T14:23:33.918391",
+        "to": ["notification:jessica"],
+        "verb": "tweet"
+      }
+    ]
+  }

packages/stream_feed/test/models_test.dart

@@ -127,25 +127,8 @@ void main() {
   });
   group('RealtimeMessage', () {
     test('fromJson', () {
-      final fromJson = RealtimeMessage.fromJson({
-        'deleted': [],
-        'deleted_foreign_ids': [],
-        'feed': 'reward:1',
-        'new': [
-          {
-            'actor': 'reward:1',
-            'foreign_id': null,
-            'id': 'f3de8328-be2d-11eb-bb18-128a130028af',
-            'message': "@Jessica check out getstream.io it's so dang awesome.",
-            'object': 'tweet:id',
-            'origin': null,
-            'target': null,
-            'time': '2021-05-26T14:23:33.918391',
-            'to': ['notification:jessica'],
-            'verb': 'tweet'
-          }
-        ]
-      });
+      final fromJson =
+          RealtimeMessage.fromJson(jsonFixture('realtime_message.json'));
 
       expect(
           fromJson,