add more read test

packages/stream_chat/test/src/core/models/read_test.dart

@@ -26,5 +26,29 @@ void main() {
         'unread_messages': 10,
       });
     });
+
+    test('copyWith', () {
+      final read = Read.fromJson(jsonFixture('read.json'));
+      var newRead = read.copyWith();
+      expect(
+        newRead.lastRead,
+        DateTime.parse('2020-01-28T22:17:30.966485504Z'),
+      );
+      expect(newRead.user.id, 'bbb19d9a-ee50-45bc-84e5-0584e79d0c9e');
+      expect(newRead.unreadMessages, 10);
+
+      newRead = read.copyWith(
+        user: User(id: 'test'),
+        lastRead: DateTime.parse('2021-01-28T22:17:30.966485504Z'),
+        unreadMessages: 2,
+      );
+
+      expect(
+        newRead.lastRead,
+        DateTime.parse('2021-01-28T22:17:30.966485504Z'),
+      );
+      expect(newRead.user.id, 'test');
+      expect(newRead.unreadMessages, 2);
+    });
   });
 }