feat: expose helpers for static models (#311)

Creating a static model is useful for testing, and the missing `public init` on `ActionModel` makes that difficult to do. This PR adds that init along with a couple static factory methods for that use case.

WorkflowSwiftUI/Sources/ActionModel.swift

@@ -1,10 +1,22 @@
 /// An ``ObservableModel`` for workflows with a single action.
 ///
-/// Rather than creating this model directly, you should use the
-/// ``Workflow/RenderContext/makeActionModel(state:)`` method to create an instance of this model.
+/// To create an accessor, use
+/// ``Workflow/RenderContext/makeActionModel(state:)``. State writes and actions
+/// will be sent to the workflow.
 public struct ActionModel<State: ObservableState, Action>: ObservableModel, SingleActionModel {
     public let accessor: StateAccessor<State>
     public let sendAction: (Action) -> Void
+
+    /// Creates a new ActionModel.
+    ///
+    /// Rather than creating this model directly, you should usually use the
+    /// ``Workflow/RenderContext/makeActionModel(state:)`` method to create an
+    /// instance of this model. If you need a static model for testing or
+    /// previews, you can use the ``constant(state:)`` method.
+    public init(accessor: StateAccessor<State>, sendAction: @escaping (Action) -> Void) {
+        self.accessor = accessor
+        self.sendAction = sendAction
+    }
 }
 
 /// An observable model with a single action.
@@ -22,3 +34,15 @@ extension ActionModel: Identifiable where State: Identifiable {
         accessor.id
     }
 }
+
+#if DEBUG
+
+public extension ActionModel {
+    /// Creates a static model which ignores all sent values, suitable for static previews
+    /// or testing.
+    static func constant(state: State) -> ActionModel<State, Action> {
+        ActionModel(accessor: .constant(state: state), sendAction: { _ in })
+    }
+}
+
+#endif

WorkflowSwiftUI/Sources/StateAccessor.swift

@@ -13,6 +13,12 @@ public struct StateAccessor<State: ObservableState> {
     let state: State
     let sendValue: (@escaping (inout State) -> Void) -> Void
 
+    /// Creates a new state accessor.
+    ///
+    /// Rather than creating this model directly, you should usually use the
+    /// ``Workflow/RenderContext/makeStateAccessor(state:)`` method. If you need
+    /// a static model for testing or previews, you can use the
+    /// ``constant(state:)`` method.
     public init(
         state: State,
         sendValue: @escaping (@escaping (inout State) -> Void) -> Void
@@ -31,3 +37,15 @@ extension StateAccessor: Identifiable where State: Identifiable {
         state.id
     }
 }
+
+#if DEBUG
+
+public extension StateAccessor {
+    /// Creates a static state accessor which ignores all sent values, suitable for static previews
+    /// or testing.
+    static func constant(state: State) -> StateAccessor<State> {
+        StateAccessor(state: state, sendValue: { _ in })
+    }
+}
+
+#endif

WorkflowSwiftUI/Sources/Store+Preview.swift

@@ -12,23 +12,17 @@ public struct StaticStorePreviewContext {
     }
 
     public func makeStateAccessor<State>(state: State) -> StateAccessor<State> {
-        StateAccessor(
-            state: state,
-            sendValue: { _ in }
-        )
+        .constant(state: state)
     }
 
     public func makeActionModel<State, Action>(
         state: State
     ) -> ActionModel<State, Action> {
-        ActionModel(
-            accessor: makeStateAccessor(state: state),
-            sendAction: makeSink(of: Action.self).send
-        )
+        .constant(state: state)
     }
 }
 
-extension Store {
+public extension Store {
     /// Generates a static store for previews.
     ///
     /// Previews generated with this method are static and do not update state. To generate a
@@ -38,15 +32,15 @@ extension Store {
     /// - Parameter makeModel: A closure to create the store's model. The provided `context` param
     ///  is a convenience to generate dummy sinks and state accessors.
     /// - Returns: A store for previews.
-    public static func preview(
+    static func preview(
         makeModel: (StaticStorePreviewContext) -> Model
     ) -> Store {
         let context = StaticStorePreviewContext()
         let model = makeModel(context)
         let (store, _) = make(model: model)
         return store
     }
-    
+
     /// Generates a static store for previews.
     ///
     /// Previews generated with this method are static and do not update state. To generate a
@@ -55,14 +49,14 @@ extension Store {
     ///
     /// - Parameter state: The state of the view.
     /// - Returns: A store for previews.
-    public static func preview<State, Action>(
+    static func preview<State, Action>(
         state: State
     ) -> Store<ActionModel<State, Action>> where Model == ActionModel<State, Action> {
         preview { context in
             context.makeActionModel(state: state)
         }
     }
-    
+
     /// Generates a static store for previews.
     ///
     /// Previews generated with this method are static and do not update state. To generate a
@@ -71,7 +65,7 @@ extension Store {
     ///
     /// - Parameter state: The state of the view.
     /// - Returns: A store for previews.
-    public static func preview<State>(
+    static func preview<State>(
         state: State
     ) -> Store<StateAccessor<State>> where Model == StateAccessor<State> {
         preview { context in