SwiftUI中依赖网络请求的ObservableObject类单元测试方案咨询

问题背景 #

使用SwiftUI开发时，通过iTunes API获取应用版本并判断是否需要更新，实现了AppUpdateViewModel类，将currentAppVersion和usersAppVersion设为私有以保证封装性，但单元测试时无法直接修改这些私有属性，导致测试受阻。

原ViewModel实现：

final class AppUpdateViewModel: ObservableObject {
    
    @Published
    private var currentAppVersion: String?
    private var usersAppVersion: String = Bundle.appVersionNumber()
    
    private func fetchCurrentAppVersion() async -> Void {
        do {
            let res = try await NetworkingManger.shared.request(.getAppMetaDataFromApple, type: AppUpdateModel.self)
            self.currentAppVersion = res.results[0].version
        } catch {
            print("app updates ERR: ", error.localizedDescription)
        }
    }
    
    public func appNeedsUpdate() -> Bool {
        guard let currentAppVersionParts = currentAppVersion?.split(separator: ".") else { return false }
        let curAppVersMajor = currentAppVersionParts[0]
        let curAppVersMinor = currentAppVersionParts[1]
        let curAppVersPatch = currentAppVersionParts[2]
        
        let userAppVersionParts = usersAppVersion.split(separator: ".")
        let userAppVersMajor = userAppVersionParts[0]
        let userAppVersMinor = userAppVersionParts[1]
        let userAppVersPatch = userAppVersionParts[2]
        
        return ( curAppVersMajor > userAppVersMajor ||
                 (curAppVersMajor == userAppVersMajor && curAppVersMinor > userAppVersMinor) ||
                 (curAppVersMajor == userAppVersMajor && curAppVersMinor == userAppVersMinor && curAppVersPatch > userAppVersPatch) )
    }
}

测试时遇到的问题：无法直接修改私有属性currentAppVersion和usersAppVersion。

解决方案 #

1. 提取版本比较逻辑到独立工具类（优先推荐） #

版本比较是纯业务逻辑，与ViewModel的状态管理无关，将其抽离为独立工具类后，可直接测试该类的逻辑，无需依赖ViewModel的私有属性。

步骤：

• 创建版本比较工具类：

struct VersionComparator {
    static func needsUpdate(currentVersion: String, userVersion: String) -> Bool {
        // 先校验版本格式合法性
        guard let currentParts = currentVersion.split(separator: ".").map(String.init), currentParts.count == 3,
              let userParts = userVersion.split(separator: ".").map(String.init), userParts.count == 3 else {
            return false
        }
        
        let curMajor = currentParts[0], curMinor = currentParts[1], curPatch = currentParts[2]
        let userMajor = userParts[0], userMinor = userParts[1], userPatch = userParts[2]
        
        return curMajor > userMajor ||
               (curMajor == userMajor && curMinor > userMinor) ||
               (curMajor == userMajor && curMinor == userMinor && curPatch > userPatch)
    }
}

• 修改ViewModel，调用工具类方法：

final class AppUpdateViewModel: ObservableObject {
    
    @Published
    private var currentAppVersion: String?
    private var usersAppVersion: String = Bundle.appVersionNumber()
    
    private func fetchCurrentAppVersion() async {
        do {
            let res = try await NetworkingManger.shared.request(.getAppMetaDataFromApple, type: AppUpdateModel.self)
            self.currentAppVersion = res.results[0].version
        } catch {
            print("app updates ERR: ", error.localizedDescription)
        }
    }
    
    public func appNeedsUpdate() -> Bool {
        guard let currentVersion = currentAppVersion else { return false }
        return VersionComparator.needsUpdate(currentVersion: currentVersion, userVersion: usersAppVersion)
    }
}

• 测试工具类：

final class VersionComparatorTests: XCTestCase {
    func testPatchUpdateNeeded() {
        let result = VersionComparator.needsUpdate(currentVersion: "1.0.5", userVersion: "1.0.4")
        XCTAssertTrue(result)
    }
    
    func testNoUpdateNeeded() {
        let result = VersionComparator.needsUpdate(currentVersion: "1.0.3", userVersion: "1.0.4")
        XCTAssertFalse(result)
    }
    
    func testMinorUpdateNeeded() {
        let result = VersionComparator.needsUpdate(currentVersion: "1.2.0", userVersion: "1.1.5")
        XCTAssertTrue(result)
    }
}

2. 依赖注入（测试ViewModel完整流程） #

如果需要测试ViewModel的完整流程（包括网络请求后判断更新），可以通过依赖注入替换真实的网络管理器和版本来源，避免直接修改私有属性。

步骤：

• 定义网络请求协议，让NetworkingManger遵循该协议：

protocol NetworkingProtocol {
    func request<T: Decodable>(_ endpoint: Endpoint, type: T.Type) async throws -> T
}

extension NetworkingManger: NetworkingProtocol {}

• 修改ViewModel，添加支持依赖注入的初始化方法：

final class AppUpdateViewModel: ObservableObject {
    
    @Published
    private var currentAppVersion: String?
    private let usersAppVersion: String
    private let networkingManager: NetworkingProtocol
    
    // 初始化方法：默认使用真实依赖，测试时传入Mock实例
    init(networkingManager: NetworkingProtocol = NetworkingManger.shared, userVersion: String = Bundle.appVersionNumber()) {
        self.networkingManager = networkingManager
        self.usersAppVersion = userVersion
    }
    
    private func fetchCurrentAppVersion() async {
        do {
            let res = try await networkingManager.request(.getAppMetaDataFromApple, type: AppUpdateModel.self)
            self.currentAppVersion = res.results[0].version
        } catch {
            print("app updates ERR: ", error.localizedDescription)
        }
    }
    
    public func appNeedsUpdate() -> Bool {
        guard let currentVersion = currentAppVersion else { return false }
        return VersionComparator.needsUpdate(currentVersion: currentVersion, userVersion: usersAppVersion)
    }
}

• 创建Mock网络管理器，返回测试用的版本数据：

class MockNetworkManager: NetworkingProtocol {
    func request<T: Decodable>(_ endpoint: Endpoint, type: T.Type) async throws -> T {
        // 返回预设的版本数据
        let mockUpdateModel = AppUpdateModel(results: [AppUpdateResult(version: "1.0.5")])
        return mockUpdateModel as! T
    }
}

• 测试ViewModel完整流程：

final class AppUpdateViewModelTests: XCTestCase {
    func testAppNeedsUpdateAfterFetch() async {
        // 注入Mock网络管理器和测试用户版本
        let vm = AppUpdateViewModel(networkingManager: MockNetworkManager(), userVersion: "1.0.4")
        // 调用版本获取方法
        await vm.fetchCurrentAppVersion()
        // 验证更新判断结果
        XCTAssertTrue(vm.appNeedsUpdate())
    }
}

3. 使用@testable导入（不推荐，仅临时场景） #

通过@testable导入目标模块，可以访问模块内的私有成员，但这会破坏封装性，仅适合临时测试或特殊场景。

测试代码示例：

@testable import YourAppModule

final class AppVersionTests: XCTestCase {
    var appUpdateVM: AppUpdateViewModel!
    
    override func setUp() {
        super.setUp()
        appUpdateVM = AppUpdateViewModel()
    }
    
    func testPatchUpdate() {
        // 直接修改私有属性
        appUpdateVM.currentAppVersion = "1.0.5"
        appUpdateVM.usersAppVersion = "1.0.4"
        
        XCTAssertTrue(appUpdateVM.appNeedsUpdate())
    }
}

总结 #

• 优先选择提取纯逻辑到工具类，既保证封装性，又能单独测试核心业务逻辑；
• 若需测试ViewModel完整流程，使用依赖注入替换真实依赖，模拟网络请求和版本来源；
• @testable导入仅作为临时方案，长期来看会降低代码的可维护性。

内容的提问来源于stack exchange，提问作者Trey6