TestStore & long running effect

[gkaimakas]

Hey good people!

I have a Reducer that starts a long running effect when the view appears (with SwiftUI's .task modifier)

...
case .task:
let effA = .run { send in /// runs once
      await .send(.fetchObjsCompleted(Result(catching: {
         /// fetch some data
      }))
   }

let effB = .run { send in /// is long living
      for await _ in objCreatedAsyncStream {
        await .send(.fetchObjsCompleted(Result(catching: {
          /// fetch some data
        }))
      }
   }

return .concatenate(
   effA,
   effB
)
...

The rationale behind all that is that I want to fetch an initial batch of data, but also to subscribe to notifications from objCreatedAsyncStream and when an event is emitted, refresh the data.

I was able to test the initial fetching of data using TestStore but when I try to test the long running effect I'm facing issues. I want to return an empty array of objs from effA and once objCreatedAsyncStream emits an event, return an array with some objects.

let store = TestStore(initialState: State()) {
    MyReducer()
} withDependencies: {
    $0.fetchData = { [] }
} 

await store.send(.task)
await store.receive(\.fetchObjsCompleted.success) {
    /// check that effA returns an empty array
}

/// effB is still running at this point

store.dependencies.fetchData = { [objA] }

objCreatedAsyncStream.send(value: objA) // a new event is emitted

await store.receive(\.fetchObjsCompleted.success) {
    /// check that effB return [objA]
}

I thought that I could swap the dependency that fetches the data during the test, but it seems that swapping a dependency with a long running effect, is not supported.

Any ideas on how to approach this?

[pyrtsa]

I'd introduce a local variable let data = LockIsolated<[MyObject]>([]) next to the TestStore and, instead of ever reassigning store.dependencies.fetchData, simply initialise it to $0.fetchData = { data.value } and change data between assertions.

[gkaimakas]

That worked like a charm! Thanks @pyrtsa