Use Json data file on Flutter unit test

Question

I would like to do the unit test for model by Flutter. Then I want to use test json data.

But I got the error message.
type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>' in type cast

I want to know how to solve this issue.

Here is the test codes.

void main() {
  group('Gift Test', () {
    test('Gift model test', () {
      final file = File('json/gift_test.json').readAsStringSync();
      final gifts = Gift.fromJson(jsonDecode(file) as Map<String, dynamic>);

      expect(gifts.id, 999);
    });
  });
}

Here is the model

@freezed
abstract class Gift with _$Gift {
  @Implements(BaseModel)
  const factory Gift({
    int id,
    String name,
    int amount,
    Image image,
  }) = _Gift;

  factory Gift.fromJson(Map<String, dynamic> json) => _$GiftFromJson(json);
}

And this is the test data.

[
  {
    "id": 999,
    "name": "testest",
    "amount": 30000,
    "image": {
      "id": 9999,
      "image": {
        "url": "https://text.jpg",
      },
    },
  }
]

The problem is that in the json file you have a List so dart is inferring it is a List<dymanic> you can either remove the [] from the /gift_test.json, or iterate over it and do a test over each one item. — Wilson Toribio
– Wilson Toribio, Commented Apr 14, 2022 at 13:54

Valentin Vignal · Accepted Answer · 2022-04-14 13:57:49Z

1

Your json file is a list, not an object, either you change your json file in

  {
    "id": 999,
    "name": "testest",
    "amount": 30000,
    "image": {
      "id": 9999,
      "image": {
        "url": "https://text.jpg",
      },
    },
  }

Or you will need to update your code to take the first element of the list:

final file = File('json/gift_test.json').readAsStringSync();
final gifts = Gift.fromJson((jsonDecode(file) as List).first as Map<String, dynamic>);

answered Apr 14, 2022 at 13:57

Valentin Vignal

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2 Comments

Masaya Over a year ago

Thank you for your answer. It works! Why do I have to cast the List?

Valentin Vignal Over a year ago

Your Json file has its object inside a list (your file starts with [ and ends with ]). So when you decode it, you get a List and you need to cast it to be able to use .first on it.

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