Hello, I got a `Flow` like ```flow { while (true) { emit(something) delay(interv...

# coroutines

[Davide Giuseppe Farella]

Hello, I got a Flow like

flow {
    while (true) {
        emit(something)
        delay(interval)
    }
}.flowOn(injectedDispatcher)

In my test, I inject the dispatcher and test like

val result = mutableListOf<Int>()
val interval = 30.seconds
val flow = getSavedCredentials(interval)
val job = launch {
    flow.toList(result)
}

repo.add(1)
advanceTimeBy(interval)

repo.add(2)
advanceTimeBy(interval)

repo.add(3)
advanceTimeBy(interval)

So I would expect result to be [ 1 ], [ 1, 2 ], [ 1, 2, 3 ]
But instead it is [ 1, 2, 3 ], [ 1, 2, 3 ], [ 1, 2, 3 ]

What’s wrong with it? 😵

[gildor]

try not exact number, 30 for flow, use a bit gap between, like advanceTimeBy(interval + 5.seconds)

[Davide Giuseppe Farella]

Same 😞

[gildor]

could you provide a complete example on Kotlin Playground?

[Davide Giuseppe Farella]

Sure, let me try to reproduce without dependants to project

[Davide Giuseppe Farella]

Can I use coroutines-test on Playground?

[Davide Giuseppe Farella]

🤔

[Davide Giuseppe Farella]

May that help?

Untitled

[Davide Giuseppe Farella]

message has been deleted

[gildor]

Can I use coroutines-test on Playground? (edited)

Yes

[Davide Giuseppe Farella]

How to? Deps are not resolved 😵

[gildor]

ahh, TestCoroutineDispatcher wouldn’t be available, indeed, worth to request adding it to Junit run configuration

[Davide Giuseppe Farella]

So is there something I can do? 🙂

[gildor]

Yes

[gildor]

it’s because of closure of mutable property

[gildor]

Change

emit(something)

With

emit(something.toList())

[gildor]

What is happening, is that by time when flow lambda is invoking, repo alredy changed, essentially when you call repo += 3 flow is not even dispatched, because it’s blocking code (mutating repo) but launch and flow are asyncronous

[gildor]

also, to make your test pass, swap emit and delay, otherwise flow will emit empty list

[Davide Giuseppe Farella]

Oh… This is tricky!! So that’s given by our mock! The signature of the method is Map , but our test implementation is a MutableMap under the hood!

[Davide Giuseppe Farella]

Thank you!

[Davide Giuseppe Farella]

also, to make your test pass, swap emit and delay, otherwise flow will emit empty list

Yup, noticed, May be better to delay the collecting