Test reducer who run task is taking too long

[yuyuUI]

Hi, I am happy that Effect can adapt async await with .run. But in test, I found test is going to take more time.

Only one file add to Tests/ComposableArchitectureTests/THE_FILE.swift from 4aab217

**_Click to expand Source code_**

import ComposableArchitecture
private struct AsyncEnv {
  var getValue: () async -> Int
}

private struct Env {
  var getValue: () -> EffectTask<Int>
}

private enum AsyncEnvKey: DependencyKey {
  static let liveValue = AsyncEnv(getValue: { 42 })
  static let testValue = AsyncEnv(getValue: { 4200 })
}

private enum EnvKey: DependencyKey {
  static let liveValue = Env(getValue: { .run(operation: { send in await send(42) }) })
  static let testValue = Env(getValue: { .init(value: 420) })
}

private extension DependencyValues {
  var asyncEnv: AsyncEnv {
    get { self[AsyncEnvKey.self] }
    set { self[AsyncEnvKey.self] = newValue }
  }

  var env: Env {
    get { self[EnvKey.self] }
    set { self[EnvKey.self] = newValue }
  }
}

private struct Feature: ReducerProtocol {
  @Dependency(\.asyncEnv) var asyncEnv
  @Dependency(\.env) var env
  struct State: Equatable { var value = 0 }
  enum Action: Equatable { case tapForAsync, tap, receive(Int) }
  func reduce(into state: inout State, action: Action) -> EffectTask<Action> {
    switch action {
    case let .receive(value):
      state.value = value
      return .none
    case .tap:
      return env.getValue()
        .map(Action.receive)
    case .tapForAsync:
      return .task {
        .receive(
          await asyncEnv.getValue()
        )
      }
    }
  }
}

import XCTest

@MainActor
final class AsyncTests: XCTestCase {
  func testWithAsync() async throws {
    let reducer = Feature()

    let store = TestStore(
      initialState: Feature.State(),
      reducer: reducer
    )

    await store.send(.tapForAsync)
    await store.receive(.receive(4200)) {
      $0.value = 4200
    }
  }

  func testWithoutAsync() throws {
    let reducer = Feature()

    let store = TestStore(
      initialState: Feature.State(),
      reducer: reducer
    )

    store.send(.tap)
    store.receive(.receive(420)) {
      $0.value = 420
    }
  }

  func testWithoutAsyncInAsyncTest() async throws {
    let reducer = Feature()

    let store = TestStore(
      initialState: Feature.State(),
      reducer: reducer
    )

    await store.send(.tap)
    await store.receive(.receive(420)) {
      $0.value = 420
    }
  }
}

Xcode runs the test successfully. But the one using () async -> Int took 0.10 seconds

Test Suite 'Selected tests' started at 2023-05-26 11:38:27.788
Test Suite 'ComposableArchitectureTests.xctest' started at 2023-05-26 11:38:27.788
Test Suite 'AsyncTests' started at 2023-05-26 11:38:27.788
Test Case '-[ComposableArchitectureTests.AsyncTests testWithAsync]' started.
Test Case '-[ComposableArchitectureTests.AsyncTests testWithAsync]' passed (0.010 seconds).
Test Case '-[ComposableArchitectureTests.AsyncTests testWithoutAsync]' started.
Test Case '-[ComposableArchitectureTests.AsyncTests testWithoutAsync]' passed (0.001 seconds).
Test Case '-[ComposableArchitectureTests.AsyncTests testWithoutAsyncInAsyncTest]' started.
Test Case '-[ComposableArchitectureTests.AsyncTests testWithoutAsyncInAsyncTest]' passed (0.003 seconds).
Test Suite 'AsyncTests' passed at 2023-05-26 11:38:27.803.
	 Executed 3 tests, with 0 failures (0 unexpected) in 0.014 (0.014) seconds
Test Suite 'ComposableArchitectureTests.xctest' passed at 2023-05-26 11:38:27.803.
	 Executed 3 tests, with 0 failures (0 unexpected) in 0.014 (0.015) seconds
Test Suite 'Selected tests' passed at 2023-05-26 11:38:27.803.
	 Executed 3 tests, with 0 failures (0 unexpected) in 0.014 (0.015) seconds
Program ended with exit code: 0

Even the one from swift test --filter AsyncTests

Test Suite 'Selected tests' started at 2023-05-26 11:38:10.116
Test Suite 'swift-composable-architecturePackageTests.xctest' started at 2023-05-26 11:38:10.117
Test Suite 'AsyncTests' started at 2023-05-26 11:38:10.117
Test Case '-[ComposableArchitectureTests.AsyncTests testWithAsync]' started.
Test Case '-[ComposableArchitectureTests.AsyncTests testWithAsync]' passed (0.005 seconds).
Test Case '-[ComposableArchitectureTests.AsyncTests testWithoutAsync]' started.
Test Case '-[ComposableArchitectureTests.AsyncTests testWithoutAsync]' passed (0.000 seconds).
Test Case '-[ComposableArchitectureTests.AsyncTests testWithoutAsyncInAsyncTest]' started.
Test Case '-[ComposableArchitectureTests.AsyncTests testWithoutAsyncInAsyncTest]' passed (0.002 seconds).
Test Suite 'AsyncTests' passed at 2023-05-26 11:38:10.124.
	 Executed 3 tests, with 0 failures (0 unexpected) in 0.007 (0.007) seconds
Test Suite 'swift-composable-architecturePackageTests.xctest' passed at 2023-05-26 11:38:10.124.
	 Executed 3 tests, with 0 failures (0 unexpected) in 0.007 (0.007) seconds
Test Suite 'Selected tests' passed at 2023-05-26 11:38:10.124.
	 Executed 3 tests, with 0 failures (0 unexpected) in 0.007 (0.008) seconds

Do I miss any config? Or is it normal?

[mbrandonw]

Hi @yuyuUI, I'm not sure I understand. From the logs you provided it seems all of your tests took less than 0.01 seconds. That seems quite fast.

It is true that async tests take a little longer, due to the Swift concurrency runtime, and async tests in TestStore take a little longer due to our necessary use of megaYield and the fact that Swift does not offer the tools necessary to reliably test async code.

We are working on some tools to speed things up, but the code you shared does not seem to really have many problems,.

[yuyuUI]

Thanks! I have tried some tests but can not reproduce the one that takes too long. I can see my test speed up from 3.5 seconds to 0.02 seconds by using the EffectTask facade, like { .run(operation: { send in await send(42) }) } in the code sample.

Appreciate your effort.

[stephencelis]

@yuyuUI This is the unfortunate reality of async code in Swift. Custom executors may help in the future, and as @mbrandonw mentioned, we are working on code that utilizes this and will hopefully bring your 3.5 second test runs back down closer to 0.02 in the future.