我如何模拟 URLSession？

Question

我正在查看用 Swift 4 编写的 iOS 应用程序。它有一个使用 URLSession 的相当简单的网络层，但是该应用程序没有单元测试，在我开始重构之前，我我热衷于通过引入一些测试来解决这个问题。

在执行此操作之前，我必须能够模拟 URLSession，这样我就不会在测试期间创建真实的网络请求。我在当前实施中看不到如何实现这一目标？我在测试中注入 URLSession 的入口点在哪里。

我提取了网络代码并使用相同的逻辑创建了一个简单的应用程序，如下所示：

Endpoint.swift

import Foundation

protocol Endpoint {
    var baseURL: String { get }
}

extension Endpoint {
    var urlComponent: URLComponents {
        let component = URLComponents(string: baseURL)
        return component!
    }

    var request: URLRequest {
        return URLRequest(url: urlComponent.url!)
    }
}

struct RandomUserEndpoint: Endpoint {
    var baseURL: String {
        return RandomUserClient.baseURL
    }
}

APIClient.swift

import Foundation

enum Either<T> {
    case success(T), error(Error)
}

enum APIError: Error {
    case unknown, badResponse, jsonDecoder
}

enum HTTPMethod: String {
    case get = "GET"
    case put = "PUT"
    case post = "POST"
    case patch = "PATCH"
    case delete = "DELETE"
    case head = "HEAD"
    case options = "OPTIONS"
}

protocol APIClient {
    var session: URLSession { get }
    func get<T: Codable>(with request: URLRequest, completion: @escaping (Either<T>) -> Void)
}

extension APIClient {
    var session: URLSession {
        return URLSession.shared
    }

   func get<T: Codable>(with request: URLRequest, completion: @escaping (Either<T>) -> Void) {
        let task = session.dataTask(with: request) { (data, response, error) in
            guard error == nil else { return completion(.error(error!)) }
            guard let response = response as? HTTPURLResponse, 200..<300 ~= response.statusCode else { completion(.error(APIError.badResponse)); return }

            guard let data = data else { return }

            guard let value = try? JSONDecoder().decode(T.self, from: data) else { completion(.error(APIError.jsonDecoder)); return }

            DispatchQueue.main.async {
                completion(.success(value))
            }
        }
        task.resume()
    }

}

RandomUserClient.swift

import Foundation

class RandomUserClient: APIClient {
    static let baseURL = "https://randomuser.me/api/"

    func fetchRandomUser(with endpoint: RandomUserEndpoint, method: HTTPMethod, completion: @escaping (Either<RandomUserResponse>)-> Void) {
        var request = endpoint.request
        request.httpMethod = method.rawValue
        get(with: request, completion: completion)
    }

}

RandomUserModel.swift

import Foundation

typealias RandomUser = Result

struct RandomUserResponse: Codable {
    let results: [Result]?
}

struct Result: Codable {
    let name: Name
}

struct Name: Codable {
    let title: String
    let first: String
    let last: String
}

使用此代码的一个非常简单的应用程序可能类似于

class ViewController: UIViewController {

    let fetchUserButton: UIButton = {
        let button = UIButton(type: .system)
        button.setTitle("FETCH", for: .normal)
        button.setTitleColor(.black, for: .normal)
        button.titleLabel?.font = UIFont.boldSystemFont(ofSize: 36)
        button.addTarget(self, action: #selector(fetchRandomUser), for: .touchUpInside)
        button.translatesAutoresizingMaskIntoConstraints = false
        button.isEnabled = true
        return button
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .white

        view.addSubview(fetchUserButton)
        NSLayoutConstraint.activate([
            fetchUserButton.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            fetchUserButton.centerYAnchor.constraint(equalTo: view.centerYAnchor),
        ])
    }

    @objc func fetchRandomUser() {
        let client = RandomUserClient()
        fetchUserButton.isEnabled = false
        client.fetchRandomUser(with: RandomUserEndpoint(), method: .get) { [unowned self] (either) in
            switch either {
            case .success(let user):
                guard let name = user.results?.first?.name else { return }
                let message = "Your new name is... \n\(name.first.uppercased()) \(name.last.uppercased())"
                self.showAlertView(title: "", message: message)
                self.fetchUserButton.isEnabled = true
            case .error(let error):
                print(error.localizedDescription)
            }
        }
    }

    func showAlertView(title: String, message: String) {
        let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertController.Style.alert)
        alert.addAction(UIAlertAction(title: "Close", style: UIAlertAction.Style.default, handler: nil))
        self.present(alert, animated: true, completion: nil)
    }
}

理想情况下，我想要一种模拟 URLSession 的方法，这样我就可以正确地测试它，但是我不确定如何使用当前代码实现它。

Answer 1

在这种情况下，如果您在 RandomUserClient 左右断言实际上可能更有意义。

你扩展 RandomUserClient 并让它接受一个 URLSession 的实例，它本身被注入你的 APIClient.

class RandomUserClient: APIClient {
    var session: URLSession
    static let baseURL = "https://randomuser.me/api/"

    init(session: URLSession) {
        self.session = session
    }

    func fetchRandomUser(with endpoint: RandomUserEndpoint, method: HTTPMethod, completion: @escaping (Either<RandomUserResponse>)-> Void) {
        var request = endpoint.request
        request.httpMethod = method.rawValue

        get(with: request, session: session, completion: completion)
    }

}

您的视图控制器需要更新，以便 RandomUserClient 被初始化为 lazy var client = RandomUserClient(session: URLSession.shared)

您的 APIClient 协议和扩展也需要重构以接受新注入的 URLSession 依赖项

protocol APIClient {
    func get<T: Codable>(with request: URLRequest, session: URLSession, completion: @escaping (Either<T>) -> Void)
}

extension APIClient {
    func get<T: Codable>(with request: URLRequest, session: URLSession, completion: @escaping (Either<T>) -> Void) {
        let task = session.dataTask(with: request) { (data, response, error) in
            guard error == nil else { return completion(.error(error!)) }
            guard let response = response as? HTTPURLResponse, 200..<300 ~= response.statusCode else { completion(.error(APIError.badResponse)); return }

            guard let data = data else { return }

            guard let value = try? JSONDecoder().decode(T.self, from: data) else { completion(.error(APIError.jsonDecoder)); return }

            DispatchQueue.main.async {
                completion(.success(value))
            }
        }
        task.resume()
    }

}

注意添加 session: URLSession。

我如何模拟 URLSession？

How can I mock URLSession?

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