Flutter Unit Testing: Some tests pass, while other similar tests fail

Question

I have a firestore database class, which I am trying to test. I have multiple objects which can be saved to different collections depending on the path provided. While testing the creation of an Item document and a Review object document - the Item object test passes and the Review object test fails, despite being almost identical tests. Here is some sample code:

///FirestoreService class - setData method
///I have an updated version of this method with a .catchError((e) => false);
///I have added it below, but I may be wrong on the syntax, I am adding this 
///from memory as I am not at my regular workspace at the moment

Future<bool> setData(

  {bool isAdd = false, String path, Map<String, dynamic> data}) async {

if (isAdd) {

  await Firestore.instance.collection(path).add(data).catchError((e) => false);

  print('$path: $data');

} else {

  final reference = Firestore.instance.document(path);

  print('$path: $data');

  await reference.setData(data).catchError((e) => false);

}
return true;

}

///FirestoreDatabase class

/// Paths.items() = "items"; references collection 'items'
/// Paths.reviews() = "reviews"; references collection 'reviews'

final _service = FirestoreService.instance;

FirestoreService set(FirestoreService service) => _service = service;


  @override

  Future<bool> addItem(Item item) async => await _service.setData(

      isAdd: true, path: Paths.items(), data: item.toMap());


  @override

  Future<bool> addReview(Review review) async => await _service.setData(

      isAdd: true, path: Paths.reviews(), data: review.toMap());

And the tests:

class MockFirestoreService extends Mock implements FirestoreService {}

main() {
  MockFirestoreService service;
  FirestoreDatabase db;
  Item item;
  Review review;

  setup() {
    service = MockFirestoreService();
    db = FirestoreDatabase();
    db.set(service); //Use the mock firestore service

    item = Item(id: 'abc', name: 'abc', description: 'abc test');
    review = Review(id: 'def' rating: 5.0, text: 'review of abc', itemId: 'abc');
  }

  test('This test passes', () async {
    when(service.setData(isAdd: true, path: Paths.items(), data: item.toMap())
.thenAnswer((_) => Future.value(true);

    final bool result = await db.addItem(item);

    expect(result, true);
  });

test('This test fails', () async {
    when(service.setData(isAdd: true, path: Paths.reviews(), data: review.toMap())
.thenAnswer((_) => Future.value(true);

    final bool result = await db.addReview(review);

    expect(result, true);
  });
}

The first test adding a mock item passes, where as the second test adding a review fails, expecting a value of true, but returning null.

I have also tried expecting a completion:

expect(db.setReview(review), completion(expect(true)));

I am failing to understand why one test passes, yet the other fails. Any help, or improvements to my code is appreciated! Thanks!

Answer 1

I normally do like this and have no problem: Set the mock functions, then assign the mock object right after that. For example:

 when(service.setData(isAdd: true, path: Paths.items(), data: item.toMap())
   .thenAnswer((_) => Future.value(true);
 db.set(service);