While TestStore.scope was an interesting experiment, and we utilized it in our Tic-Tac-Toe demo to test view state, there are a couple awkward things it introduces that make us think it should be on the chopping block:

1. The feature makes TestStore a pretty intense type: it has five generics 😱

   swift-composable-architecture/Sources/ComposableArchitecture/TestSupport/TestStore.swift

   Line 170 in b8dddaf

   public final class TestStore<State, LocalState, Action, LocalAction, Environment> {

   In general it's a lot to take in, and simplifying things would make the type more approachable.

2. Scoped test stores have an awkward matrix of what level you're at during an assertion:

   Assertion	Action Type	State Type
   send	✅ Local	✅ Local
   receive	❌ Global	✅ Local

   Received actions come from effects and not the view, so it doesn't make sense to receive view actions...but this mismatch is pretty trippy.

A cursory search on GitHub doesn't find much public use, but we were wondering if anyone following the repo takes advantage of this feature privately, and how heavily invested in it they may be.

There are a few alternate ways we find that folks test view state and actions:

• Unit test them manually as data:

  XCTAssertEqual(
    ViewState(State(...)), // Test view state init'd with `State`
    ViewState(...)         // against view state init'd manually
  )
  
  XCTAssertEqual(
    ViewAction(.action),   // Test view action init'd with `Action`
    ViewAction.action      // against view action init'd manually
  )

  This is simple, but completely separated from reducer logic that produces the state in the first place, for better and/or worse.

• Unit test them manually in an otherwise unscoped TestStore:

  // Test view action before sending it to the store:
  store.send(ViewAction(.action)) { $0.state = updatedState }
  
  // Test view state after store state has been updated:
  XCTAssertEqual(ViewState(store.state), ViewState(...))

  This gives users the ability to get view state/action coverage in a normal TestStore test.

• Test using a view store, instead:

  let viewStore = ViewStore(
    store.scope(state: ViewState.init, action: ViewAction.init)
  )
  viewStore.send(.action)
  XCTAssertEqual(viewStore.state, ViewState(...))

  This focuses on the "view" aspect of this data, which means you lose test store affordances like testing exhaustivity and effects, but that might be how you want to focus on this aspect of testing.

Given the awkwardness of TestStore.scope and the availability of these less awkward alternatives, we think it's OK to deprecate, but would like to hear from you! We'll be rolling out an update soon with deprecation warnings in order to solicit more feedback (linking here).