Flutter unit testing streams that do map - flutter

Question

I did stuck with testing streams that do some transformations before returning the value. I am using Firestore as my data storage and have a separated data layer that performs some mapping from DocumentSnapshot<T> to my model. Here is an example of the repo:
class RequestsRepository {
final CollectionReference<Request> _requestsCollection =
getIt<FirebaseFirestore>().collection('requests').withConverter<Request>(
fromFirestore: (snapshot, _) => Request.fromJson(snapshot.data()!),
toFirestore: (request, _) => request.toJson());
Stream<Request?> observe(String id) {
return _requestsCollection
.doc(id)
.snapshots()
.map((snapshot) => snapshot.exists ? snapshot.data() : null);
});
}
}
And now I'd like to cover observe(id) function with tests. Here is the solution I came to and below I'll explain why:
test('request exists', () async {
// WHEN
final stream = repository.observe(request.id);
// expected events
final events = [null, request, request..completed = true, null];
var eventIndex = 0;
// THEN
stream.listen(expectAsync1((value) async {
await Future.delayed(Duration(milliseconds: 100));
expect(value, events[eventIndex]);
eventIndex++;
}, max: -1));
// GIVEN
await firestore
.collection('requests')
.doc(request.id)
.set(request.toJson());
request.completed = true;
await firestore
.collection('requests')
.doc(request.id)
.set(request.toJson());
// reset request data
request.completed = false;
});
I tried emitsInOrder stream matcher however it fails, because I'm doing mapping inside the observe(id) function and that result in actually not request object but _MapStream<DocumentSnapshot<Request?>, Request?> instead because of the logic that stream map function follows:
Stream<S> map<S>(S convert(T event)) {
return new _MapStream<T, S>(this, convert);
}
The solution I came to did work for this case but it did not for other tests and also the solution is smelly. Any suggestions how to tests these kind of streams?
UPDATE:
Per comment from #pskink here is the demo test that fails with the same reason:
class Test {
Stream<B> observe() {
return Stream.periodic(Duration(milliseconds: 500), (i) => A(i * 10))
.map((i) => B('s${i.a}'));
}
}
class A {
final int a;
A(this.a);
bool operator ==(o) => o is A && a == o.a;
int get hashCode => a.hashCode;
}
class B {
final String b;
B(this.b);
bool operator ==(o) => o is B && b == o.b;
int get hashCode => b.hashCode;
}
void main() {
test('mapped stream: A > B', () async {
final stream = Test().observe();
expect(stream, emitsInOrder([B('s0'), B('s10'), B('s20'), B('s30')]));
});
}
It passes with the test so far.

Answer 1

Thanks to #pskink so far to identifying that the issue is not with stream conversion (even though logs look pretty unreadable). I had to make my Request object Equatable so it can now compare all fields appropriately. And I had to remove the await from firestore calls so that events occur really asynchronously.
Here is an example of working test:
test('request exists', () async {
// GIVEN
final timestamp = DateTime.now();
final request = Request(
'49a257e1-c0e3-4cc1-9053-aaf55197f897',
user.id,
"${user.firstName} ${user.lastName}",
user.phone ?? "",
'center',
'comment',
timestamp,
false,
false);
await firestore
.collection('requests')
.doc(request.id)
.set(request.toJson());
// WHEN
final stream = repository.observe('id', request.id);
// THEN
expect(
stream,
emitsInOrder([
Request(
'49a257e1-c0e3-4cc1-9053-aaf55197f897',
user.id,
"${user.firstName} ${user.lastName}",
user.phone ?? "",
'center',
'comment',
timestamp,
false,
false),
Request(
'49a257e1-c0e3-4cc1-9053-aaf55197f897',
user.id,
"${user.firstName} ${user.lastName}",
user.phone ?? "",
'center',
'comment',
timestamp,
false,
true),
]));
firestore
.collection('requests')
.doc(request.id)
.set({"completed": true}, SetOptions(merge: true));
});