RxSwift/RxTest 如何使用 Observable 返回測試異步 function

Question

我對 RxSwift 很陌生，我試圖創建一些單元測試。 在這種情況下，我想測試從實時數據庫 Firebase 獲取對象是否正確發生。

func getAllPosts() -> Observable<[PostItem]> {
      ref = Database.database().reference()
        return Observable.create { observer -> Disposable in
        
        self.ref.child("Posts").observe(.value) { (snapshot) in
            var postsList:[PostItem] = []
            for child in snapshot.children {
                let snap = child as! DataSnapshot
                
            let postDict = snap.value as! [String: Any]
                let postAux = PostItem(id: snap.ref.key ?? "", authorId: postDict["authorId"] as? String  ?? "", name: postDict["name"] as? String  ?? "", content: postDict["content"] as? String  ?? "", createAt: postDict["createAt"] as? String  ?? "")
            postsList.append(postAux)
            }
            observer.onNext(postsList)
        }
        
    return Disposables.create {}
    }
}

問題是 firebase 的返回是異步的，我嘗試測試的方式在返回之前完成。

func testFetchPosts() throws {
    
    let newsAPIService = NewsAPIService()
    let posts = newsAPIService.fetchNewsFromAPI()
    
    XCTAssertNil(posts, "The posts is nil")
}

Obs：我嘗試使用 XCTest 期望，但我不知道是否實現不正確或者它是否真的不起作用

謝謝！

Answer 1

我建議您將邏輯移出 Observable.create 以便您可以獨立測試它。 像這樣的東西：

func getAllPosts() -> Observable<[PostItem]> {
    return Observable.create { observer in
        // note that you don't have to store this value. The disposable will hold it for you.
        let ref = Database.database().reference()
        // the `handleSnapshot(observer:)` function is defined below.
        ref.child("Posts").observe(.value, handleSnapshot(observer: observer))
        // make sure you turn off the observation on dispose.
        return Disposables.create { ref.stop() }
    }
}

您的邏輯應該在一個單獨的高階 function 中：

// note that this is a free function. It should not be defined inside any class or struct.
// I'm guessing on the `Snapshot` type. I don't use Firebase.
func handleSnapshot(observer: AnyObserver<[PostItem]>) -> (Snapshot) -> Void {
    { snapshot in
        var postsList: [PostItem] = []
        for child in snapshot.children {
            let snap = child as! DataSnapshot

            let postDict = snap.value as! [String: Any]
            let postAux = PostItem(id: snap.ref.key ?? "", authorId: postDict["authorId"] as? String  ?? "", name: postDict["name"] as? String  ?? "", content: postDict["content"] as? String  ?? "", createAt: postDict["createAt"] as? String  ?? "")
            postsList.append(postAux)
        }
        observer.onNext(postsList)
    }
}

測試這個 function 很容易：

func testShapshotHandler() throws {
    let scheduler = TestScheduler(initialClock: 0)
    let observer = scheduler.createObserver([PostItem].self)
    let snapshot = Snapshot(children: [Child()]) // create a snapshot object here
    let sut = handleSnapshot(observer: observer.asObserver())

    sut(snapshot)

    // assumes `PostItem` is Equatable
    XCTAssertEqual(observer.events, [.next(0, [PostItem(id: "", authorId: "", name: "", content: "", createAt: "")])])
}

---

如果你對高階函數感到不舒服，你可以這樣做：

func getAllPosts() -> Observable<[PostItem]> {
    return Observable.create { observer in
        let ref = Database.database().reference()
        ref.child("Posts").observe(.value) { snapshot in
            observer.onNext(handle(snapshot: snapshot))
        }
        return Disposables.create { ref.stop() }
    }
}

func handle(snapshot: Snapshot) -> [PostItem] {
    var postsList: [PostItem] = []
    for child in snapshot.children {
        let snap = child as! DataSnapshot

        let postDict = snap.value as! [String: Any]
        let postAux = PostItem(id: snap.ref.key ?? "", authorId: postDict["authorId"] as? String  ?? "", name: postDict["name"] as? String  ?? "", content: postDict["content"] as? String  ?? "", createAt: postDict["createAt"] as? String  ?? "")
        postsList.append(postAux)
    }
    return postsList
}

現在測試邏輯更加容易了。 您不再需要測試調度程序或觀察員。