Fix Xcode15.3 (Swift5.10) warning/Swift 6 error: Main actor-isolated class 'XXXTests' has different actor isolation from nonisolated superclass 'XCTestCase'; this is an error in Swift 6 (#97)

* Move MainActor attribute from subclass of XCTestCase to each function because different actor isolation from nonisolated superclass will be compiler error in Swift6

* Move MainActor attribute from class to func on Exmaple/Tests

* Fix sample code of testing on README.md

Author: kntkymt

Examples/Packages/CrossPlatform/Tests/ExampleCounterTests/ExampleCounterTests.swift

@@ -3,8 +3,8 @@ import XCTest
 
 @testable import ExampleCounter
 
-@MainActor
 final class ExampleCounterTests: XCTestCase {
+    @MainActor
     func testCounterAtom() {
         let context = AtomTestContext()
         let atom = CounterAtom()

Examples/Packages/CrossPlatform/Tests/ExampleTodoTests/ExampleTodoTests.swift

@@ -3,7 +3,6 @@ import XCTest
 
 @testable import ExampleTodo
 
-@MainActor
 final class ExampleTodoTests: XCTestCase {
     let completedTodos = [
         Todo(
@@ -30,6 +29,7 @@ final class ExampleTodoTests: XCTestCase {
         completedTodos + uncompleteTodos
     }
 
+    @MainActor
     func testFilteredTodosAtom() {
         let context = AtomTestContext()
         let atom = FilteredTodosAtom()
@@ -53,6 +53,7 @@ final class ExampleTodoTests: XCTestCase {
         XCTAssertEqual(context.watch(atom), uncompleteTodos)
     }
 
+    @MainActor
     func testStatsAtom() {
         let context = AtomTestContext()
         let atom = StatsAtom()

Examples/Packages/iOS/Tests/ExampleMapTests/ExampleMapTests.swift

@@ -4,8 +4,8 @@ import XCTest
 
 @testable import ExampleMap
 
-@MainActor
 final class ExampleMapTests: XCTestCase {
+    @MainActor
     func testLocationObserverAtom() {
         let atom = LocationObserverAtom()
         let context = AtomTestContext()
@@ -25,6 +25,7 @@ final class ExampleMapTests: XCTestCase {
         XCTAssertFalse(manager.isUpdatingLocation)
     }
 
+    @MainActor
     func testCoordinateAtom() {
         let atom = CoordinateAtom()
         let context = AtomTestContext()
@@ -40,6 +41,7 @@ final class ExampleMapTests: XCTestCase {
         XCTAssertEqual(context.watch(atom)?.longitude, 2)
     }
 
+    @MainActor
     func testAuthorizationStatusAtom() async {
         let atom = AuthorizationStatusAtom()
         let manager = MockLocationManager()

Examples/Packages/iOS/Tests/ExampleMovieDBTests/ExampleMovieDBTests.swift

@@ -3,8 +3,8 @@ import XCTest
 
 @testable import ExampleMovieDB
 
-@MainActor
 final class ExampleMovieDBTests: XCTestCase {
+    @MainActor
     func testImageAtom() async {
         let apiClient = MockAPIClient()
         let atom = ImageAtom(path: "", size: .original)
@@ -29,6 +29,7 @@ final class ExampleMovieDBTests: XCTestCase {
         XCTAssertEqual(failurePhase.error as? URLError, error)
     }
 
+    @MainActor
     func testMovieLoader() async {
         let apiClient = MockAPIClient()
         let atom = MovieLoaderAtom()
@@ -61,6 +62,7 @@ final class ExampleMovieDBTests: XCTestCase {
         }
     }
 
+    @MainActor
     func testMyListAtom() {
         let atom = MyListAtom()
         let context = AtomTestContext()
@@ -80,6 +82,7 @@ final class ExampleMovieDBTests: XCTestCase {
         XCTAssertEqual(context.watch(atom).movies, [.stub(id: 1)])
     }
 
+    @MainActor
     func testIsInMyListAtom() {
         let context = AtomTestContext()
 
@@ -89,6 +92,7 @@ final class ExampleMovieDBTests: XCTestCase {
         XCTAssertFalse(context.watch(IsInMyListAtom(movie: .stub(id: 1))))
     }
 
+    @MainActor
     func testCastsAtom() async {
         let apiClient = MockAPIClient()
         let atom = CastsAtom(movieID: 0)
@@ -113,6 +117,7 @@ final class ExampleMovieDBTests: XCTestCase {
         XCTAssertEqual(failurePhase.error as? URLError, error)
     }
 
+    @MainActor
     func testSearchMoviesAtom() async throws {
         let apiClient = MockAPIClient()
         let atom = SearchMoviesAtom()

Examples/Packages/iOS/Tests/ExampleTimeTravelTests/ExampleTimeTravelTests.swift

@@ -3,8 +3,8 @@ import XCTest
 
 @testable import ExampleTimeTravel
 
-@MainActor
 final class ExampleTimeTravelTests: XCTestCase {
+    @MainActor
     func testTextAtom() {
         let context = AtomTestContext()
         let atom = InputStateAtom()

Examples/Packages/iOS/Tests/ExampleVoiceMemoTests/ExampleVoiceMemoTests.swift

@@ -5,8 +5,8 @@ import XCTest
 
 @testable import ExampleVoiceMemo
 
-@MainActor
 final class ExampleVoiceMemoTests: XCTestCase {
+    @MainActor
     func testIsRecordingAtom() {
         let context = AtomTestContext()
         let atom = IsRecordingAtom()
@@ -18,6 +18,7 @@ final class ExampleVoiceMemoTests: XCTestCase {
         XCTAssertTrue(context.read(atom))
     }
 
+    @MainActor
     func testRecordingDataAtom() {
         let context = AtomTestContext()
         let atom = RecordingDataAtom()
@@ -55,6 +56,7 @@ final class ExampleVoiceMemoTests: XCTestCase {
         XCTAssertTrue(context.watch(IsRecordingFailedAtom()))
     }
 
+    @MainActor
     func testRecordingElapsedTimeAtom() async {
         let context = AtomTestContext()
         let atom = RecordingElapsedTimeAtom()
@@ -79,6 +81,7 @@ final class ExampleVoiceMemoTests: XCTestCase {
         XCTAssertEqual(context.watch(atom), .success(10))
     }
 
+    @MainActor
     func testToggleRecording() {
         let context = AtomTestContext()
         let actions = VoiceMemoActions(context: context)
@@ -125,6 +128,7 @@ final class ExampleVoiceMemoTests: XCTestCase {
         XCTAssertNil(context.watch(RecordingDataAtom()))
     }
 
+    @MainActor
     func testDelete() {
         let context = AtomTestContext()
         let actions = VoiceMemoActions(context: context)
@@ -142,6 +146,7 @@ final class ExampleVoiceMemoTests: XCTestCase {
         XCTAssertFalse(context.watch(IsPlayingAtom(voiceMemo: voiceMemo)))
     }
 
+    @MainActor
     func testIsPlayingAtom() {
         let context = AtomTestContext()
         let audioPlayer = MockAudioPlayer()
@@ -167,6 +172,7 @@ final class ExampleVoiceMemoTests: XCTestCase {
         XCTAssertTrue(context.watch(IsPlaybackFailedAtom()))
     }
 
+    @MainActor
     func testPlayingElapsedTimeAtom() async {
         let context = AtomTestContext()
         let voiceMemo = VoiceMemo.stub()

README.md

@@ -1240,7 +1240,7 @@ In order to fully test your app, this library guarantees the following principle
 
 In the test case, you first create an `AtomTestContext` instance that behaves similarly to other context types. The context allows for flexible reproduction of expected scenarios for testing using the control functions described in the [Context](#context) section.  
 In addition, it's able to replace the atom value with test-friendly dependencies with `override` function. It helps you to write a reproducible & stable testing.  
-Since atom needs to be used from the main actor to guarantee thread-safety, `XCTestCase` class that tests atoms should have `@MainActor` attribute.
+Since atom needs to be used from the main actor to guarantee thread-safety, functions that tests atoms should have `@MainActor` attribute.
 
 <details><summary>Click to expand the classes to be tested</summary>
 
@@ -1293,8 +1293,8 @@ struct FetchBookAtom: ThrowingTaskAtom, Hashable {
 
 ```swift
 
-@MainActor
 class FetchBookTests: XCTestCase {
+    @MainActor
     func testFetch() async throws {
         let context = AtomTestContext()
         let api = MockAPIClient()

Tests/AtomsTests/Atom/AsyncSequenceAtomTests.swift

@@ -2,8 +2,8 @@ import XCTest
 
 @testable import Atoms
 
-@MainActor
 final class AsyncSequenceAtomTests: XCTestCase {
+    @MainActor
     func testValue() async {
         let pipe = AsyncThrowingStreamPipe<Int>()
         let atom = TestAsyncSequenceAtom { pipe.stream }
@@ -67,6 +67,7 @@ final class AsyncSequenceAtomTests: XCTestCase {
         }
     }
 
+    @MainActor
     func testRefresh() async {
         let pipe = AsyncThrowingStreamPipe<Int>()
         let atom = TestAsyncSequenceAtom { pipe.stream }
@@ -130,6 +131,7 @@ final class AsyncSequenceAtomTests: XCTestCase {
         }
     }
 
+    @MainActor
     func testUpdated() async {
         let pipe = AsyncThrowingStreamPipe<Int>()
         var updatedValues = [Pair<Int?>]()

Tests/AtomsTests/Atom/ModifiedAtomTests.swift

@@ -2,8 +2,8 @@ import XCTest
 
 @testable import Atoms
 
-@MainActor
 final class ModifiedAtomTests: XCTestCase {
+    @MainActor
     func testKey() {
         let base = TestAtom(value: 0)
         let modifier = SelectModifier<Int, String>(keyPath: \.description)
@@ -17,6 +17,7 @@ final class ModifiedAtomTests: XCTestCase {
         XCTAssertNotEqual(AnyHashable(atom.key).hashValue, AnyHashable(base.key).hashValue)
     }
 
+    @MainActor
     func testValue() async {
         let base = TestStateAtom(defaultValue: "test")
         let modifier = SelectModifier<String, Int>(keyPath: \.count)

Tests/AtomsTests/Atom/ObservableObjectAtomTests.swift

@@ -2,7 +2,6 @@ import XCTest
 
 @testable import Atoms
 
-@MainActor
 final class ObservableObjectAtomTests: XCTestCase {
     @MainActor
     final class TestObject: ObservableObject {
@@ -30,6 +29,7 @@ final class ObservableObjectAtomTests: XCTestCase {
         }
     }
 
+    @MainActor
     func test() async {
         let atom = TestAtom()
         let context = AtomTestContext()
@@ -112,6 +112,7 @@ final class ObservableObjectAtomTests: XCTestCase {
         }
     }
 
+    @MainActor
     func testUpdated() async {
         var updatedObjects = [TestObject]()
         let atom = TestAtom { object, _ in